Hi Lynda
It was the same way here in Singapore. Fingerprinting was directed to the police department according to the embassy website.
You could either download the FD258 from FBI site, get your fingerprints taken (2 sets) and send them alongside with your application, or USCIS will mail you two sets of blank ones.
Either way, you will need to send the full payment of the biometrics.
Better do some research on where you can get it done in the UK.
Good luck!
Thank you again for answering my questions. You are really generous. Even a lot of immigration lawyers are no familiar with this process in Asia. Really appreciate it.