Re: So how on earth am I supposed to get bitcoins in the UK?

Convert your funds to euros and wire tranfer to bitcoin-central.net EUR account:
Account Holder Name: Paymium (Paymium is the registered company operating bitcoin-central, instwawire, instawallet and Paytunia)
IBAN: FR76 3006 6108 8700 0200 7310 542
BIC: CMCIFRPP

If you do not want to convert, send GBP to Paymium's account in GBP .
Your bitcoin-central account will be credited in Euro at the going rate when we receive the funds.
IBAN: FR76 3006 6108 8700 0200 7310 930
BIC: CMCIFRPP

In any case, since the UK is in the SEPA zone, the wire transfer is free.
There is a 15 fee only if you mistakenly send euros to a GBP account or vice versa.
Do not forget to copy your bitcoin-central account number (BC-XXX..) in the "comments" field of your wire transfer online form.

Which banks allow SEPA transactions for free? Natwest trying to charge me £25!

Heh, same with Barclays, from what I've read. I'm not convinced the UK *is* actually in the SEPA zone, but only just started looking into it...

I must confirm that the simplest is to convert GBP to EUR first, then send the funds (in EUR) to Paymium EUR account. That's a SEPA wire transfer, free of charge. You only pay a currency conversion fee applied by the bank of origin (in the UK).
A wire transfer in GBP would not be considered SEPA (yet).