Nobody memorises their sort code, and the moment you need it is usually the moment you cannot find a statement. The good news is that a UK bank has to make the number available to you, and there are four places it reliably appears. The bad news is that the fifth place people look, an old card or an old letter, is the one most likely to be out of date.
The app, on the screen built for sharing
Every UK banking app has a screen whose entire purpose is handing your sort code and account number to someone who wants to pay you. It is usually called account details, payment details or something close, and it often offers to copy both fields or share them as an image. This is the most current source you have, because it reads from the bank's own record rather than from something printed months ago. If your app shows a nickname rather than the account name, that screen will normally show the real account name too.
The statement header
A statement, paper or electronic, carries the sort code and account number in the header along with the account name and the bank's registered office. That makes it the single most useful document when a form wants all of those fields at once, which employers and foreign banks frequently do. Use a recent one: if you have switched accounts or the bank has migrated a product, an older statement can carry details that no longer route anywhere useful.
A cheque book or paying in slip, if you still have one
Cheques carry the sort code and account number along the bottom in the machine readable band, and paying in slips carry them on the face. Both are perfectly good sources provided the book belongs to the account you are asking about and the account has not been changed since. Fewer people have either these days, which is why the app has become the default answer, but a cheque book in a drawer is a valid source and does not require logging in.
Asking the bank, and why it is sometimes the right move
If you are being asked for details to receive a large or unusual payment, or the details you have are contradicting each other, telephone or message the bank and have them confirm the pair. It takes a few minutes and it eliminates the risk of sending someone a number from a closed account. It is also the only route that works if you have lost access to the app and have no recent statement, which is more common after a change of phone than people expect.
Questions people ask about what is my sort code
Is my sort code on my debit card?
Sometimes. Older cards print it under the cardholder name, and several UK banks now issue cards with no printed account details at all.
Does my sort code change?
It can, if your bank migrates your account to a different product or a different part of the group. Read it from the app or a recent statement rather than assuming.
Is it safe to give out my sort code?
It is the pair people need in order to pay you, and it appears on invoices and cheques routinely. Be careful about who you give it to along with other personal details, and never in response to an unexpected request.
Why do I have two sort codes?
Because you hold two accounts, or because a savings product sits on a different code from your current account. Each account has its own pair.