Just ordered The Polytunnel Book: Fruit and Vegetables All Year Round"
Russell, Joyce;
Looking at several poly tunnel companies. Probably get a 8'x15' or might be able to squeeze in an 8'x20' tunnel, to go along with my 4 raised beds 3mx1.3m and 6'x6' greenhouse. Looking to provide veg year round. Would the size of tunnel be sufficient to provide a steady stream of veg??

What does the book advise?

Don't know, aint arrived yet ;-)

The only thing I would have misgivings about is the ammount of extra time required to achieve 'Year round veg'
Gardening under glass or polythene is very abour intensive, especially with regards to watering.
Even though it may be chucking it down outdoors, indoors you could be weilding a watering can every day!

that's when complicated water arrangement comes in....water butts, plus slightly sloping seep hoses and your work is done [when it's raining anyway]

It's an excellent book. That's a massive tunnel you are getting, brilliant. By looking at the photos I think her's is probably in the range of only 10M x 4M (mine is 6M x 3M so I'm just judging against the photos). I don't think the point of the book is about being self-sufficient as such so she doesnt recommend a size. It's about how to grow year round and what can be grown year round (early and late stuff as well as normal growing times of course).
But that size would definately give you a 'steady stream' of veg. You're in for a treat. You could get a proper rotation going with decent sized beds and have plenty of space for permanant planting like fruit trees and bushes, grape vines, a pond etc

I've just bought that book too, it suggests the crops for AYR growing.