suggestions of a good book or other to learn about investments etc

Eyeful

As for IHT are these of any help?

https://moneytothemasses.com/tax/inheritance-tax/the-10-best-ways-to-avoid-inheritance-tax

https://www.thetimes.co.uk/money-mentor/answer/reduce-inheritance-tax/

https://monevator.com/pensions-and-inheritance-tax/

badger09

I doubt a single book will cover everything and some frequently mentioned are aimed at the American market. 
I’d recommend monevator.com as a starting point. It’s a series of articles, regularly updated, covering a wide range of subjects. It’s written in non jargon terms & you can always ask questions here if you need help. 

Good luck