According to AAMC (the MCAT test maker), there are 1 MCAT test centers in United Kingdom. Most testing centers are located inside a college or university. You can select a testing location that is nearest to you. Please note that you are able to choose a test center when registering for the MCAT.
CITY OF LONDON, UNITED KINGDOM #1
PROMETRIC, 2ND FLOOR
9 CLOAK LANE
LONDON, United Kingdom EC4R 2RU