Not sure if you meant 'trumps' or 'turnips'.
I'd have thought 'that book' might have said something about this 'industry'? - I can't check - book is on loan to a cousin and anyway mine is an old edition now.
I reckon these businesses are separate from one another but may use the same supplier. One of the biggest is this one, but there are many others.
http://www.howdens.com/
Note that they make a virtue out of only supplying to the trade.
The biggest issue by far is the design - do you know exactly what you want? I don't just mean the units but the way in which they will fit around existing fixed features like windows and doors. The way the flying shelves will work over the recesses - where to put the lighting - that sort of thing.
I reckon I know a fair bit about housebuilding - I project-managed my own build, and personally did a heck of a lot of the work myself. But I wouldn't (even if Mrs BM would have let me) have designed or built the kitchen. I was staggered when we went to a decent designer and he shared with me some of the issues that he thought about regarding how the design went together.
So the thing about these design companies is the decent ones can make the difference between how the thing looks at the end.
Then there's the carcases. Most of these are made in big sheds, not hand-made - and its the quality of the things you can't obviously see that is worth looking for - thickness and density of the material, hinges, proper backs, not flimsy. The better manufacturers produce the modules in a wider range of sizes etc. - enabling the designer to have more scope in design.
(cont)