http://www.hpac.co.uk/
You can either send it into them, and have it sent back to yourself after testing (if the bottle pass the test) or take it down to an event they will be present at like the masters.
For price, give them a ring first, its normally around £22 for testing (not sure what current prices are, so please do not quote me on that) plus return postage if your sending it in, which works out approx £40.
Best thing to do is take it down to an event (UKMasters), save on postage. If you cannot attend, get someone you know and trust to take down for you. Pick up at next event.
You can have your bottle tested any time during its life, even before the test date runs out.