In a trading update, the supermarket chain says it has decided to slow the final stage of Tesco Bank systems migration "to ensure it is as smooth as possible for customers and staff".

The decision follows problems encountered during the summer, when it transferred savings and loans products in-house from its old joint venture with the Royal Bank of Scotland to a new core banking platform from Fiserv. This left some customers unable to get to their accounts online and caused a surge in complaints that overwhelmed its call centre operations.

The next stage in the roll-out calls for the introduction of mortgages and current accounts to the new platform, but this is now set to be delayed until "early 2012".

"We have taken the decision to slow down the introduction of new products until we have settled in the new bank team, processes and systems, having encountered some technical issues during the summer, which resulted in some customers being unable to access online accounts for a short period," says the retailer.

The decision has financial implications for the business, with Tesco hacking £40 million off its internal profit projections as it absorbs double running costs during the extended transition period.

The banking business has also added £57 million in provisioning for alleged mis-selling of payment protection insurance dating back to its joint venture with RBS, raising the total provision £92 million.

Including the provisioning, trading profit for the banking business during the first half was down 65.9% to £44 million as the company noted only small digit marginal pick-ups in customer account numbers.