I would definitely learn to improve on your English. Even if you know how to drive, if you can't communicate or know what other people are talking about you can get into a lot of unnecessary problems.
The book I would recommend for you to get is the following:
https://www.dvsabooks.com/car-theory-bookThe book above will contain all the possible MCQ questions that will pop up in the exam. If you memorise all the answers to the questions, then you should be able to do OK. This shouldn't take more than 2 weeks.
The book needs to be the latest edition, but it doesn't need to be brand new. Try to get a copy second hand if you can for about £10. The brand new copies tend to go for £15.00