This is copied directly off HMRC, A direct bank transfer to HMRC bank accounts is NOT instant. HMRC no longer use Bank of England accounts they now use Natwest bank as do I so I called on Thursday to check, they confirmed 3 working days. Note the last bit FPS not available.
You can use your bank/building society services to pay by internet or telephone banking. To make the payment you will need the HMRC bank account details given below and your Self Assessment reference number, also referred to as your Unique Taxpayer Reference (UTR).
If you don’t have access to internet or telephone banking but wish to make a transfer by other means, your bank may accept telephone, fax or written instructions.
If you pay using any of these methods, your bank will transfer your money direct to HMRC’s bank account.
It normally takes three bank working days for payment to reach HMRC. Bank working days are Monday to Friday excluding bank holidays. Some banks and building societies can take longer. You should check with your bank or building society to see how long they take to transfer payment and what their cut-off time is for initiating payment. If they take longer then you will need to initiate your payment earlier.
Note: HMRC is unable to make or receive payments using the Faster Payment Service (FPS)