Just another thought...What does your friend want to try and grow?
If it is fruit and veg then that would suggest very different books from a person who wants to grow pretty annual flowers from seed /or perenials/or shrubs/ or bulbs/or ferns or to have a rockery/or a pond/or a wild life garden.
I'm not keen on books by celebrity gardeners, so for around £20, New, you could do a lot worse than these RHS guides by Chris Brickell... all links to Amazon...
My favourite gardening reference book is by the late great Christopher LLoyd - 'The Well tempered garden' Not many pictures, but full of great advice in all garden aspects
A gardener's work is never at an end - (John Evelyn 1620-1706)
@ Yorkshirerose - that is my favourite gardening book too, re-read over and over, just for the pleasure of it.
Only managed to make it to Great Dixter once, a year or two before he died, but it all seemed so familiar from reading this book! My daughter and I loved it, but my father found it all hard to fathom - the late summer untidiness of long grass and the exuberant planting was too much for him. Though he wasn't a gardener, he loved photographing them, but I don't think he knew where to start on GD!
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I still use this old museum piece...
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'The Well tempered garden' Not many pictures, but full of great advice in all garden aspects
Titchmarsh book.