The following information on UKCAT Help is taken from The Ultimate UKCAT Guide: 1200 Practice Questions
Booking your Test
Unless there are strong reasons otherwise, you should try to book your test during August. This is because in the summer, you should have plenty of time to work on the UKCAT and not be tied up with schoolwork or your personal statement deadline. If you book it any earlier, you’ll have less time for your all-important preparation; if you book any later, you might get distracted with schoolwork, your personal statement deadline and the rest of your UCAS application. In addition, you pay £15 more to sit the test on or after 1 September.
Many students find sections 3 and 4 the easiest to improve on. Initially, they can often be the hardest sections, but with a bit of familiarity and practice their score can increase greatly. If you start your preparation late or have limited time for any reason, it would be wise to concentrate most on these sections in order to achieve the best gains.
Using your UKCAT Score
Different medical schools use UKCAT in different ways – so use this to your advantage! If you score well on UKCAT, you may increase your chances of success by choosing medical schools which use it as a major component of the application process. On the other hand, if your score isn’t so good, you may prefer to opt for universities that don’t look at your UKCAT score, or ones that use it as a more minor consideration.
By making choices after finding out your score, you can increase your chance of getting a place.