Investec has launched a new one-year fixed-rate Isa paying a table-topping rate of 4.2 per cent.

The deal is available to new customers who open Investec Save's Isa from today.

It has leapfrogged Harpenden Building Society in our independent This is Money savings tables, which pays 4.12 per cent, making it the clear best buy one-year Isa. 

It's good news for savers who have been suffering the effects of the Bank of England base rate being cut to 3.75 per cent in December, which has helped savings rates tumble. 

The Isa can be opened with a deposit starting from £1,000. A saver opening this account with Investec Save would receive £420 of interest on a £10,000 deposit over one year. 

The Isa can only be opened and managed online and money must be added to the account within seven days of opening it.

All deposits kept in a cash Isa are tax free. Savers can put up to £20,000 in a cash Isa in each tax year and savers have one month from today to use their full £20,000 Isa allowance for this tax year. 

From the 2027/27 tax year, savers will only be able to keep £12,000 in a cash Isa if they are under the age of 65 due to rule changes in the Budget in a bid to encourage cash savers with large cash sums to invest. 

The Investec Isa does not currently accept transfers in from other Isas, which will be a drawback to savers who have a fixed-rate deal which is maturing or who want to lock away some of their Isa savings kept in an easy-access Isa. 

Harpenden Building Society's Isa, the next best deal paying 4.12 per cent, allows transfers in from other Isas - although it only accepts customers from certain postcodes.

Customers can hold a maximum of £1million in Investec's fixed-deal but only up to £120,000 will be protected under the Financial Services Compensation Scheme which Investec's Isa is fully covered by. 

Interest is calculated daily and paid annually into the account linked with the Isa when it was opened. 

On non-Isa accounts, there are currently two accounts paying more than 4.2 per cent, which come from Union Bank of India and Chetwood Bank.