Image caption NatWest has told customers that credit is available to those affected

About 600,000 payments that failed to enter the accounts of RBS customers overnight may not be completed until the end of the week, the bank has said.

Payments of wages, tax credits and disability living allowance were among those that failed to be credited to accounts.

RBS initially said some payments were "missing", but it had now identified and fixed the underlying problem.

Delayed payments would be processed "no later than Saturday", it said.

Such a timescale was declared "unacceptable" by the chairman of an influential committee of MPs.

In 2012, the RBS group was hit by a major IT meltdown that led to a large fine.

Image copyright PA Image caption Banks including RBS and NatWest are affected

Customers from RBS, NatWest, Coutts and Ulster Bank - all part of the same banking group - have been affected by the latest issue, which was caused by a segment of information not being inputted into the system.

Some 600,000 transactions were delayed and the banking group said it was now trying to update accounts as a "priority".

"We are aware of an issue which has resulted in a delay to payments and direct debits being applied to some customer accounts," said a spokesman for RBS.

"We have fixed the underlying issue, we apologise for the inconvenience caused and we are working flat out to get these payments updated for our customers no later than Saturday.

"To any customers concerned about the implications of this issue, we advise them to come into a branch or get in touch with our call centres, where our staff will be ready to help. We will ensure no customers are left out of pocket as a result of this issue."

Some customers reported waiting up to an hour for an answer from the bank's call centre, on calls which could be charged at a geographic rate. The bank said it was experiencing a "high volume of calls".

HM Revenue and Customs (HMRC), which oversees some benefits payments, said that some tax credits and child benefit payments had not gone through, and that those affected should contact their bank.

'This could leave my pub short of beer'

Image copyright Craig Peacock

Publican Craig Peacock, who runs The Barleycorn Inn in Wiltshire, conducts his business banking through NatWest.

"I have got bills to pay and this needs to be sorted, quickly," he said.

"I run a small pub and bed and breakfast and have to pay every Wednesday for my beer delivery to come, so I might be beerless this weekend at this rate!

"I found out about the problem when I checked the account this morning. The payments overnight hadn't gone through. Then I read the news.

"I waited over an hour on the phone to NatWest. I gave up, with the volume of calls they are getting and the phone bill rising."

He said Saturday - by which time all payments should be processed - was "ages away".

Previous problems

Penny Lanning, from Peterborough, has two children and is living with a disability.

"I am currently very poorly in hospital and was rather panicky when I discovered via mobile banking that my tax credits had not gone in. It is so stressful," she told the BBC.

"My husband has been phoning me, panicking about finance."

Another customer told the BBC: "Missing a tax credit payment and then a 30-minute wait on the NatWest helpline with no answer."

The problem only affected a relatively small proportion of payments, the bank said.

However, it is an embarrassment for the group which was fined £56m by regulators after a software upgrade in June 2012 left millions of customers unable to access accounts.

On that occasion, the IT failure affected more than 6.5 million customers in the UK over several weeks. The banking group said it had invested hundreds of millions of pounds to improve its computer systems since then.

Andrew Tyrie, who chairs the Commons Treasury committee, commenting on the latest IT failure, said: "Many thousands of individuals and businesses have once again been badly hit. Customers that have suffered loss should be reimbursed in full by RBS. It is also important that credit scores remain unaffected.

"RBS is suggesting that the delayed payments will be processed no later than Saturday. This looks unacceptable.

"Restoration of payments should be a top priority. It is crucial for those in the greatest financial need and also those who find it difficult to go to a branch."