The consensus that I have seen on gardening forums, and which I concur with, is:
The Vegetable and Herb Expert” by Dr. D.G. Hessayon – see prices on BookBrain
There are numerous books in the same series, and they all take the same format. Excellent presentation of the salient facts which make them idea reference books, as well as guiding newcomers.
You may want something more detailed that discusses the pros and cons, and discusses associated topics (such as composting, plant raising in greenhouses, digging, and so on). I’m keen on
“Grow your own Vegetables” by Joy Larkcom – see prices on BookBrain
and well worth looking at the main Web Forums where a huge bunch of friendly gardeners will give advice freely. Finding an experience gardener locally would be of great benefit to a Newbie too, go and see how they tend their allotment and listen to their sage advice – but don’t let hem send you to stores for “Two greased nuts and a long weight” !!