Just repeating what's already been said, but it all depends .....
Do you have any other savings, using up your PSA, if not, then the Santander 123 account is a good bet (currently paying 3%, minus a £5 monthly charge) - even though the rate might drop soon, 'cos if you've got £20k to put in, it'll prob still beat any other accounts. If you've more, you can open up a joint account and put another £20k in there.
I closed my old ISA and did exactly what I said above. If the rates start to climb (although I can't see it happening anytime soon), your ISA allowance is now £15 240, so it won't take too long to get it back to max.