Practical Guide to Inspection, Testing and Certification of Electrical Installations, 4th ed by Chris Kitcher. I had his first book when doing some courses.
It covers essential testing and trouble shooting and useful for more than just your first courses.
He has some good videos on youtube that accompany the book and explains things well.
Get an onsite guide, students guide to the IET wiring regulations and a level 2 City & Guilds 2365 Course text book. Don't buy any more until you get to college. Some you may be able to get from your local library.
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