Three million NatWest and RBS Isa account holders will have their rates cut or boosted, as the banks are moving anyone with an old Isa to a newer deal.
The new tax year began on Saturday, but savers who want to put their money into a new Isa should do it quickly, as some of the best buys have already been pulled.
Coventry Building Society is closing its best buy cash Isa, so act now if you want to take advantage of the account, which currently pays 2.8% AER, with a 0.6% bonus for a year.
Britain's biggest building society is urging the Government to use next month's Budget to double the amount hard-pressed savers can place into cash Isas.