I don't know of a good book.
A list of all the 'officially' tested foods as of 2008, about 2,500 of them, is on David Mendosa's site (this info comes from an academic paper produced by the researchers at Sydney University.
You could print that out
http://www.mendosa.com/gilists.htm
Otherwise there is a database on the GI site. If you click on an individual entry on the database you can find more info such as the date tested(some of the older tests used methods that wouldn't be used today), where it was tested , how many subjects and whether they were diabetic or 'normal')
There are a few specifically British foods ( eg some from Tescos and Sainsburys ) but not that many.
http://www.glycemicindex.com/
Lastly there is series of GI tables for typical foods from different European cuisines including that from the UK on the Diogenes trial website. It is in excel format.
You have to be a bit careful to check the confidence code because some of the foods haven't been tested and have been assigned a nominal GI
values were assigned according to five decreasing levels of confidence:
1.Measured values for specific foods
2.Published values from published sources
3.Equivalent values where published values for similar foods existed
4.Estimated values three values selected representing low/medium/high GI
5.Nominal values assigned as 70, where no other value could be assigned with sufficient confidence
http://www.mrc-hnr.cam.ac.uk/research/g ... -and-files