What is the bank code for swift code NWBKGB2L?

This is NatWest Bank in the United Kingdom
NW = NatWest
BL = Bank
GB = Great Britain

I'm unsure what you mean by 'bank code'. You may mean the BIC routing code, you may mean the International Bank Account Number (IBAN), you may mean the domestic sort code, or you may mean the domestic account number.

If you are trying to send money to someone in the UK, ask them for all of the above; it's on every statement they get. If they can't find it, get them to ring the bank. Every account will have a different account number, and every branch has a different sort code, so I can't give you a 'correct' one.

If you're still having trouble, ring NatWest directly.