Hi, I’m a new pass. I bought the DVSA theory book and found that the questions from that made up 90% of my actual theory test. The other questions were answered by the DVSA guide for LGV drivers book. But the theory test book is more than enough to get a pass on my opinion as I didn’t read the other one too much.
For the CPC case studies test, there is also a DVSA book and I found an app on my iPhone with practice case studies on there. I didn’t buy or use anything for my CPC test but I only passed with 41 marks and it was 40 to pass! So I recommend using something for that as I believe I was very lucky!
Anyway, good luck with your journey to HGV driving. Hope it all goes well 
Hayley