Customers only for Santander's best buy ISA product

The move continues its policy of expanding its market share by cross-selling products to existing customers.

The Flexible ISA, available from both Santander and Alliance & Leicester, had consistently headed the best buy tables since it was first launched in February.

It initially offered a rate of 3.5 per cent, fixed for the first 12 months, although this was recently reduced to 3.2 per cent.

But as of this week, people will only be able to open one of the accounts if they hold their main current account with Santander or A&L, or if they switch their current account to the group.

Reza Attar-Zadeh, director of savings and investments at Santander, said: "Flexible ISA has been a fantastic success throughout the ISA season, offering customers one of the best rates on the market for their cash ISA subscription.

"This latest offering cements our continued approach of rewarding loyalty and that the more business you do with us, the more we will offer you in return."

The group's decision to limit the Flexible ISA to its current account customers is the latest in a string of initiatives to reward customer loyalty.

Earlier this year, it launched its Zero Current Account, which does not have authorised or unauthorised overdraft charges, and does not levy fees for payments that bounce, for people who have either a mortgage or investment product with it.

It also waived the 3 per cent balance transfer fee for mortgage, current account and investment customers who take out its Zero credit card, and it does not charge booking fees on mortgages for people who hold their main current account with the group.