Millions of HSBC customers were locked out of their online accounts for two days after a major technical problem with its internet banking system.

The technical issue, which started at 8am yesterday (Monday), left customers unable to check their balances or make payments.

But at 6pm today, HSBC said its online banking was back up and running. John Hackett, UK chief operating officer, said: "I’m pleased to say that we have seen a steady return of service. We will be monitoring the service very closely, should any new issues arise."

Both online and mobile banking was affected by the outage, with the bank's personal mobile banking service restored yesterday.

Many HSBC customers vented their frustration at the bank via social media, after being unable to access their online accounts.

'We apologise'

Hackett said "a complex technical issue" had affected HSBC's internet banking systems, but it was not related to hacking. He added: "I’d like to apologise once more for any inconvenience that this technical issue has caused.

"We will be waiving any fees incurred as a result of this incident; and we will be happy to help all our customers with any issues that have arisen."

An HSBC spokesperson also said customers with urgent queries could call the bank's personal telephone banking on 03457 404 404 or business telephone banking on 03457 60 60 60.

Telephone banking delays

Frustrated customers on Twitter complained of long queues for telephone banking today.

Can you get a refund if you incur fees?

Hackett has said HSBC will waive any fees incurred as a result of the issue.

If you were left unable to pay bills or make a mortgage or rent payment, for example, contact the person or company involved immediately to let them know why there was a delay, especially to ask not to apply any possible charges.

Keep bank statements and receipts, and even screenshots and photos, in case you're asked to prove it.

A spokesperson for HSBC said requests for refunds from customers who have incurred costs from other companies will be judged on a case-by-case basis. Complain directly to it and say you want a refund.

You can also use free complaints system Resolver*, which drafts a complaint letter, monitors replies and escalates to the Financial Ombudsman if necessary.