The long-awaited new "Vegetative Key to the British Flora" (by John Poland and Eric Clement) is nearing completion. BSBI are now advertising a pre-publication offer: if you order before the 17th April it will cost £20 inclusive, whereafter it will cost £25 plus p&p.
You can download a flyer for the book from the BSBI website (see the top-right-hand corner of the site).
The authors claim that (with experience) you'll be able to identify most plants within 60 seconds! (personally I'd be happy if I could get somewhere near identifying most plants within 60 hours ...)