Promissory Notes In The UK: Key Considerations For Founders

If you’re running a startup or growing an SME, cash flow can be a constant balancing act. Sometimes you need to bridge a short-term funding gap, formalise a loan from a director, or document money being advanced by an investor without getting into a lengthy finance agreement.

That’s where a promissory note can be useful.

A promissory note is often treated as a “simple” way to evidence a debt, but simple doesn’t mean risk-free. If the terms are unclear (or you use the wrong document entirely), you can end up with funding arrangements you can’t enforce, repayments you didn’t plan for, or disputes that land right when your business least needs them.

Below, we’ll break down what a promissory note is in the UK, when it makes sense for small businesses, and how to set one up so it actually protects you.

What Is A Promissory Note (And Why Do Businesses Use One)?

A promissory note is a written promise by one party (the “maker”) to pay a certain sum of money to another party (the “payee”). In practical terms, it’s a document that records a debt and the commitment to repay it.

In the UK, promissory notes are closely linked to the concept of a “negotiable instrument” and are recognised under the Bills of Exchange Act 1882 (which also covers bills of exchange and cheques). You don’t need to memorise the legislation, but it’s helpful to know that the law expects certain features for a document to operate as a true promissory note.

What Makes A Document A “Promissory Note” In The UK?

While there’s no single magic template, a promissory note usually needs to look and behave like a clear promise to pay. Common features include:

• It’s in writing (including an email or other electronic record, provided it clearly records the promise and is kept in a usable form).
• It’s signed by the borrower (or an authorised signatory for a company).
• It’s an unconditional promise to pay (not “we’ll pay if the project succeeds”).
• The amount is certain (or clearly calculable).
• The payee is identified (who is owed the money, and in many “true” promissory notes this is expressed as payable to a named person or their order, or to bearer).
• It’s payable on demand or at a fixed or determinable future time (so it’s clear when it becomes payable).

From a founder’s perspective, promissory notes are popular because they can be:

• Faster than negotiating a full finance agreement.
• Cheaper (fewer moving parts, fewer schedules).
• Flexible for short-term or “bridge” funding.
• Useful for internal funding, such as director or shareholder loans.

That said, “quick and flexible” is only helpful if the document still sets clear expectations. Many disputes happen because the note doesn’t spell out the basics: when repayment is due, whether there’s interest, and what happens if repayment is late.

When Does A Promissory Note Make Sense For Startups And SMEs?

A promissory note can be a good fit when the deal is relatively straightforward: one party lends money, the business agrees to pay it back, and everyone wants the arrangement documented clearly.

Here are common scenarios where a promissory note might be considered.

1) Director Or Shareholder Loans

Founders often inject funds into their business to cover early expenses (stock, marketing, salaries, software subscriptions) before revenue stabilises.

A promissory note can help record:

• the amount advanced to the company
• whether interest applies
• repayment timing (for example, once the company reaches a certain cash buffer)

Depending on your structure and goals, you might also want a more detailed Directors Loan Agreement, especially where the sums are significant or the repayment terms are complex.

2) Short-Term “Bridge” Funding

If you’re waiting on a funding round to close, or you’re expecting a large invoice payment and need short-term cash, a promissory note can document a bridge loan.

In these situations, clarity matters because timeframes are tight. You’ll want to be specific about:

• the maturity date (when repayment is due)
• whether early repayment is allowed without penalty
• default interest (if any) for late payment

3) Simple Business-To-Business Loans

Sometimes one business supports another (for example, a supplier relationship, a joint venture, or a connected company in a group structure).

If the arrangement is more than “a straightforward debt with repayment”, consider whether a full Loan Agreement is more appropriate, particularly if you need warranties, covenants, or detailed enforcement rights.

4) As Part Of A Wider Contract Arrangement

You might be tempted to use a promissory note to “patch” a wider commercial deal (for example, you’re paying a settlement amount over time, or you’re paying for assets in instalments).

This can work, but be careful: if there are other legal moving parts (release clauses, assignment, termination rights, dispute resolution), a promissory note on its own can leave gaps.

In those cases, it can help to align the note with your broader Contract Law position so the documents don’t contradict each other.

What Should A UK Promissory Note Include?

If you want your promissory note to do its job (reduce misunderstandings and protect your position), it needs to be more than “I owe you £X”.

Below is a practical list of terms founders and small business owners commonly include.

Core Commercial Terms

• Parties: legal names, addresses, and company numbers where relevant.
• Principal amount: the amount being lent.
• Issue date: when the note is created (and typically when the debt starts).
• Maturity date: when the full amount is due (or a repayment schedule).
• Interest: whether interest applies, the rate, and how it accrues (daily/monthly).

Repayment Mechanics (Where Disputes Commonly Start)

• Repayment method: bank transfer details, reference requirements, and when payment is treated as received.
• Early repayment: allowed or restricted, and whether any fees apply.
• Part payments: whether the lender can refuse part payments (this can matter in default scenarios).

Default And Enforcement Terms

• Events of default: for example, non-payment, insolvency events, breach of other obligations.
• Default interest: if payment is late, do you charge a higher rate?
• Acceleration: if there’s a default, does the whole amount become immediately due?
• Costs: can the lender recover reasonable legal and enforcement costs?

Practical Legal “Housekeeping” Clauses

• Governing law and jurisdiction: typically England and Wales (or Scotland, if appropriate).
• Notices: how formal notices must be delivered and when they’re deemed received.
• Assignment: whether the lender can transfer the debt to someone else (this may tie into a Deed of Assignment later).

These aren’t “nice to haves”. For founders, they’re often the difference between a promissory note that provides certainty and one that creates a messy debate when cash is tight.

Are Promissory Notes Legally Binding In The UK?

A properly drafted promissory note can be legally binding in the UK. But enforceability depends on the details.

At a high level, you want the note to satisfy the fundamentals of a binding agreement: clarity of terms, intention to create legal relations, and proper execution.

If you’re unsure what actually makes a document enforceable, it helps to understand What Makes A Contract Legally Binding because promissory notes often fail for the same reasons as other “quick” contracts: vague wording and unclear obligations.

Do You Need Consideration?

In many cases, the “consideration” (the value exchanged) is the money being advanced. So if the lender actually advances the funds (or has already done so), that will usually support enforceability.

Problems arise when:

• the promissory note is signed but the funds are never advanced
• the note is supposed to replace an earlier arrangement, but it’s unclear what it’s replacing
• the promise to pay is conditional or ambiguous

Does A Promissory Note Need To Be A Deed?

Not always. Many promissory notes operate as simple contracts.

However, there are situations where executing as a deed is considered (for example, where you want to avoid arguments about consideration, or where the circumstances are unusual). Execution formalities for deeds are stricter, so you’ll want to get this right. If you’re going down that route, it’s worth following best practice around Executing Contracts.

Who Signs For A Company?

If the borrower is a limited company, the promissory note should be signed by someone with authority to bind the company (and ideally in line with the company’s internal approvals).

This is especially important where the lender is also a director or shareholder, because conflicts of interest can arise and good record-keeping matters.

What About Time Limits To Enforce?

In general terms, most claims for money due under a simple contract are subject to a limitation period (often six years in England and Wales, although details can vary depending on the specific claim and document type).

This is another reason it’s important not to “set and forget” old debts on informal terms. If repayment is unlikely, you may need to take advice earlier rather than later.

Common Risks With Promissory Notes (And How To Reduce Them)

A promissory note can be a smart, founder-friendly tool. But it can also create unnecessary risk if you use it as a substitute for a properly structured finance deal.

Here are common issues we see, and the practical steps you can take to reduce them.

Risk 1: The Note Is Too Vague To Enforce Easily

If your promissory note doesn’t clearly state when repayment is due, you can end up arguing about whether it’s payable “on demand” or within a “reasonable time”. That uncertainty is exactly what you’re trying to avoid.

What to do: include a clear maturity date or repayment schedule, plus default terms.

Risk 2: You Use A Promissory Note When You Actually Need A Loan Agreement

Promissory notes are usually “lighter” documents. If you need security, financial reporting obligations, conditions precedent, or detailed covenants, a promissory note may be the wrong tool.

What to do: if the transaction is significant (or you’re dealing with an external lender), consider a full Loan Agreement and, where relevant, security documentation.

Risk 3: It Creates Founder Relationship Issues

When a director, friend, or early supporter lends money to the business, expectations can get blurry. Is it a loan? Is it equity? Is it repayable only if the business “makes it”?

What to do: document the arrangement clearly, and if the business has multiple founders or investors, align the funding approach with your broader governance documents (for example, a Shareholders Agreement and board approvals).

Risk 4: Interest And Repayment Terms Trigger Cash Flow Pressure

Startups often agree to repayment terms that look fine on paper but become unrealistic six months later when revenue hasn’t landed as expected.

What to do: sanity-check the repayment schedule against your cash flow forecasts, and build in flexibility where appropriate (for example, allowing repayment by instalments, or giving the company an option to prepay when it’s able).

Risk 5: You Don’t Think About Insolvency Scenarios

This is uncomfortable, but it’s part of good risk management. If the borrower becomes insolvent, the lender may become an unsecured creditor unless there is valid security in place.

What to do: consider whether the loan should be secured, and ensure your documentation is consistent and properly executed.

Risk 6: You Mix Up “Promissory Notes” With Other Funding Tools

Founders sometimes use “promissory note” to mean any document acknowledging money is owed. But there’s a difference between:

• a promissory note
• an IOU or informal acknowledgement
• a loan agreement
• a convertible instrument (which may be intended to convert into shares later)

What to do: be clear on the commercial goal first (debt only vs debt that may convert vs deferred payment), then pick the right document and tailor it properly.

Key Takeaways

• A promissory note is a written promise to pay a specified sum, and it can be a practical way for startups and SMEs to document straightforward debt.
• Promissory notes are commonly used for director loans, short-term bridge funding, and simple business-to-business lending where a full finance agreement isn’t necessary.
• Your promissory note should be clear on the amount, repayment timing, interest (if any), and what happens if payment is late or the borrower becomes insolvent.
• A promissory note can be legally binding, but enforceability depends on clear drafting and proper execution (especially when a company is signing).
• If the deal needs security, detailed covenants, or complex repayment mechanics, a promissory note may not be enough and a tailored loan agreement may be a better fit.
• Even for “simple” documents, it’s worth getting legal help to make sure the promissory note matches the real commercial deal and reduces the risk of disputes later.

If you’d like help drafting or reviewing a promissory note (or working out whether it’s the right funding document for your business), you can reach us at 08081347754 or team@sprintlaw.co.uk for a free, no-obligations chat.