Options are a bit more limited with an adjustable/TTO as it needs someone who's familiar with assembly/disassembly of the the razors. A chap called Stephen of JJ Shaves used to be a UK option for razor refurbishment but he doesn't do it any more (although I understand he still works on straight razors). Chris Spencer of Back Roads Gold is an excellent option but he's based in the US. I have a few of his razors and his work is stellar. The international part of his business operates through Etsy. A tune up of your adjustable and replate in 24k gold or platinum will be ~£120 - £20 of which will be the cost for you to send it to him and the remaining £100 is the purchase through Etsy of his service and return postage to you. It's around £15-20 cheaper if you go for a Nickel option.
If you're happy to dissemble the razor yourself and reassemble it, there are a few UK plating options available to you. The following are also options for 3 piece razors:
The Gold Plating Company Ltd are dedicated to providing top quality Gold Plating, Silver Plating, Nickel Plating and various other finishes for all metal items. We are based in Westhoughton, Bolton, Lancashire. Which is near Manchester and Preston in the North West of the UK.
thegoldplatingcompany.co.uk
He did my Karve CB and plates in 24k gold and it looks awesome.
FMJ and do Cerakote (gun coating) I'm a few different colours: