Can anyone recommend a good vegetarian cookery book?

Rose Elliot's "Complete Vegetarian Cook book. It's not fancy stuff but lots of good recipes that, like most peoples meals, are based on ringing the changes for cooking the "same old ingredients!"
It's the one I have used most over the last 30yrs. There are a number of ones for fancy cooking as well. It depends just what sort of food you are after.

Another tip, if you want to eat fish, is to cook a vegetarian meal, then add the fish on the side. Otherwise you end up staying in the meat and two veg thought process, rather than cooking a vegetarian meal.
As I'm now on my own, I tend to eat lots of stirfries with added tofu.
Do you have a Waitrose near you? They sell a really good tofu made by Taifun. It is ready to eat - we often take it on picnics - with almonds and sesame seeds in, or herbs. If there's no other protein that my grandson wants, I slice up tofu for him. He does not eat cheese.
I always have Alpro soya cream to pour over pasta instead of using milk in a sauce.

I like the Cranks recipe books, but they might be out of print now (try the dreaded Amazon). Also Delia's Vegetarian Collection, any cookbook by Rose Elliott, and the ones Sainsbury's used to do: 'Vegetarian Meals' by Rosamond Richardson and 'The Vegetarian Gourmet' by the same. Again, those are probably out of print but you might find them online.

I'm sure there are other excellent books - I often find veggie recipes in 'ordinary' recipe collections

What sort of cook are you? By which I mean do you follow recipes slavishly, or do you experiment?
I bought a copy of Mary McCartney's Food, subtitled vegetarian home cooking. Got it from the Works for £5.99 last year.
Another one I have which I use a lot is The Low GI Vegetarian Cookbook, by Dr Jennie Brand-Miller.
I have been vegetarian for over 35 years, and have lots of books but do not use many. Anything by Colin Spencer is usually good.
Rose Elliot's books tend to be a bit simplistic. She once did a pasta book. On every page she told you how to cook your pasta, so you felt like screaming at her.
Another thing to do is go on the Viva! website, where you will find lots of recipes, most of them vegan, as you do not want to overload with cheese and eggs.
I have had both a vegetarian cafe and a vegetarian guest house. I used Cranks recipe books in the cafe, as most of the people who worked for me could use them.