I gave up trying to find a UK-based PCB manufacturer for small quantities and prototypes too.
I'm all for the idea of paying "a bit more" to support UK manufacturing industry, but in this case it's never "a bit". It's "add a zero and then some".
Fact is, my business *is* UK manufacturing, and so are my customers. I just regard the bare PCB as a component just like any other, and no longer feel I "should" be using a UK PCB supplier any more than I feel I "should" be using UK-fabricated semiconductors.