Tesco has dramatically slowed down a major system migration programme at its Tesco Bank unit, following severe problems in June that locked out customers from their accounts for three days.

Tesco Bank, which is fully run by Tesco but was until 2008 a joint venture with the Royal Bank of Scotland, faced a wrath of angry consumer and business customers who were unable to access their information or make transactions during the problems. The issues were the result of the early stages of the system migration.

As Tesco Bank reported that in the first half of the year its profits fell 66 percent to £44 million during heavy investment, Tesco group chief executive Philip Clarke told shareholders the bank had had a “bit of a problem” in the summer switching over from RBS to Tesco-run technology.

Clarke, once Tesco’s IT director, said the company was “slowing down” the migration in order to ensure the changeover goes “without a hitch”. The problems the bank had experienced were “not good”, he said.

The next stages in the migration are mortgages and current accounts, which will be moved over early next year instead of the original target of this autumn. That will be followed by credit cards, the final stage.

The company said in a statement that it had “taken the decision to slow down the introduction of new products until we have settled in the new bank team, processes and systems”.

At the time of the problems in June, scores of angry Tesco Bank customers wrote on Computerworld UK about the problems they were having with accessing their money, and with reaching a customer service assistant to obtain advice. Many said they would move their money to another bank.

“Yesterday I got through to them after 50 minutes (gave up on earlier call after 40 minutes). Was told it won't work with AOL, or with Firefox if you have Private Browsing on and do not accept cookies (is this to enable them to gather information on me), but to use IE and Aobe Flash Player Plugin,” wrote one customer. “What a shambles.”

“Won't be staying with Tesco Bank, that's for sure, after this debacle,” wrote another.

Tesco today insisted the new platforms were helping its business grow, including allowing instant decisions on approval for loans, and slashing account opening times from two weeks to 10 minutes.

Tesco Group profit grew four percent in the first half of the year to £1.8 billion.