|John Poland (on right) signs a copy of his Vegetative Key|
Image: L. Marsh
Once you are ready to buy a new key, why not take a look at the website of a dedicated natural history bookseller such as the NHBS or Summerfield Books - the latter has a great range of titles and often has discounted offers on books.
I see that Poland & Clement's Vegetative Key to the British Flora is currently on special offer at £21.75 (the RRP is £24.99). So there's no reason to struggle with an ID key that you have outgrown!