Speaking from experience on both sides of the fence.......do as much as is possible before arriving on this side of the pond....
I really regretted that I did not when I first started my training, and I see that the students that have completed the study, if not the exams, have a far more relaxed attitude and it is that attitude that helps with the flying.
I have seen both sides....the schools that are happy to help as they know that the student will return after a month or so and want to fly their aircraft. Then there are the schools that create difficulty; I know of one student I spoke to only yesterday that does not want to go back to his school as they have made it very difficult to get this training records of 20 hours and his endorsed written exams.
Of course, going to a school that you are not training at it is natural to expect to be charged....I think 15 pounds is about the average rate, but it is money well spent. In addition, this way you also get a feel for the school when choosing where you want to fly when you get back your new pleather folder with your PPL
Good luck and hope to see you soon!
Nikki