See
http://www.caa.co.uk/docs/175/SRG_FCL_ApprovedFTOs.pdf . This lists all organisations approved by the CAA to conduct FI training. Print off the list, then cross-refer to their addresses in the same document.
A couple of points:
How employable do you think you'll really be in the UK with an instructor rating obtained Stateside?
There's no such thing as an 'AFI'. Neither is there a civil 'QFI' rating. You're either an FI or an FI(Restricted).