Somebody abroad has asked for your SWIFT code and you have discovered that it is not printed anywhere obvious. It is not a secret and it is not personal to you: it identifies your bank rather than your account, which is why it does not appear alongside your account number the way a sort code does. Here is where banks actually put it, and which version to hand over.
Your bank's own help page is the primary source
Because this question is asked constantly, most banks maintain a page that states their BIC and explains how to find your IBAN. In the UK, HSBC, NatWest, Nationwide, Lloyds, Bank of Scotland, the Co-operative Bank, Santander, Barclays, Monzo and Starling all publish one. The page is written for exactly your situation and is kept current by the bank itself, which makes it a better source than a lookup site that may be repeating a code from before a merger.
The app, on the international details screen
Most banking apps show the BIC alongside the IBAN on an account details or international payments screen, sometimes behind a tab you have to look for because domestic details are shown by default. This is worth using because the app shows the code for your particular account, which matters at banks that run several codes. If the app shows an IBAN only, that is usually fine: the IBAN identifies the account and the BIC is often optional within Europe.
Which version to give when there is more than one
Large banks commonly have an eight character head office code and eleven character codes for branches or business lines. Give whatever your own bank shows for your account. If the payer's form insists on eleven characters and your bank has published eight, adding XXX to the end is the conventional way to say head office, and most banks confirm this on their own page. If in doubt, ask your bank rather than the payer's bank, because yours is the one receiving.
What the payer needs besides the code
For a payment into a UK or European account they will normally need your IBAN as well, and often nothing else. For payments from some countries they will also ask for the bank name and address, for which the registered office is the right answer. They may also ask for the account name, which should be the name the account is held in rather than a nickname. Give all of it in writing in one message so nothing is transcribed twice.
Questions people ask about what is my swift code
Is my SWIFT code unique to me?
No. It identifies your bank, and often a branch or business line inside it. Your account is identified by the IBAN or the account number.
My bank shows eight characters and the form wants eleven. What do I do?
Adding XXX to an eight character code is the conventional way to indicate the head office, and most banks say so on their own page. Confirm with your bank if the payment is large.
Is the SWIFT code on my statement?
Often, where the account is used for international payments. If not, the bank's own help page and the app's international details screen will both carry it.
Do I need a SWIFT code to be paid from within the UK?
No. A domestic UK payment uses the sort code and account number. The BIC is for payments crossing a border.