Do not bother with Doc 4444 as the UK has so many differences that you will only confuse yourself. MATS 1 I would leave until you get to the college.
Get yourself some background knowledge in met, nav and navids but don't worry about the nitty gritty of the subjects yet.
You could learn the 50 aircraft types you will need to know. The details required are the ICAO designators, UK wake vortex category, number and type of engines, ceiling and speed.
Send me a pm and I'll happily supply you with the current list of aircraft and a couple of useful websites.