Rose 1989 Grasses Sedges Rushes & Ferns is for me, hands down, best ever ‘introductory guide’ to these taxa - things that don’t fit well or don’t look like anyhting in there you can then pursue through BSBI specialist handbooks.
Glad to be of help - and yes, when I go on holiday, I make an effort to ID grasses, sedges and ferns and see how many I get (over 30 grasses in Upper Teesdale last month, more than 20 sedges) - not a bad way to get better at identifying them
I bought the 3rd edition of the BSBI “Sedges” Handbook #1 and it’s terrific. Am preparing for 2022.