Jayne-Anne Gadhia makes "shocking" claims of sexism at RBS where a woman was expected to sleep with her boss

The Edinburgh-based bank has now invited whistleblowers to report sexist behaviour after describing the allegations by Britain's most powerful banker as "shocking".

Mrs Gadhia, the Government's Women in Finance champion, who lives in Edinburgh, spoke out about sexism issues she had seen in other organisations she worked for, including RBS and Norwich Union, now Aviva, as talked of her review into gender equality.

Britain's most powerful female banker previously blamed an "alpha male" culture at RBS and former bank chief Fred Goodwin's obsessive drive for growth for contributing to the lender's near collapse during the financial crisis of 2008 and 2009.

Now the 56-year-old executive who left RBS to take up an offer by Richard Branson to join Virgin Money, has told MPs that there was a "very male" and "win-lose" culture and "undoubtedly there was a pervading sexism".

Mrs Gadhia, who had previously noticed a cultural shift following its takeover of NatWest in 2000, added: "I remember a very senior woman being very upset one day telling me that she was expected to sleep with her boss.

"That sort of thing of course means there are issues for women progressing through financial services."

Responding to her comments, a spokesman for RBS said: "These allegations are shocking and are clearly unacceptable no matter how historical they may be.

"We actively encourage anyone who has experienced inappropriate behaviour to come forward so we can investigate.

"We also have a whistle blower facility where members of staff can talk in confidence."

Speaking at the Treasury Select Committee, Mrs Gadhia had earlier contrasted her RBS experience with the current culture at Virgin, saying that Richard Branson's operation have "always been very focused on equality, not just gender equality, but ethnic diversity too".

She pointed out: "I think that has led to a healthy and vibrant culture within the companies and success for the companies.

"Having worked for Virgin I haven't experienced anything other than support for the equality agenda. Previously, however, in other organisations, I have seen some issues."

She said: "I used to work for Norwich Union, now Aviva, and there was an issue back in 1994 where Norwich Union was asked to take its sales force off the road to do some retraining, and I was asked to project manage the sales force back onto the road, which I did.

"I hoped as a youngish person that I would be able to take a more senior role in that sales team subsequently, and I was told by a very senior person at Norwich Union that 'you have not got the characteristics necessary to lead a sales force'.

"I said 'what is that', and he said 'the two things you are missing are a thick skin and a load of bull'.

"It didn't make me feel it was sexist at the time, I felt disappointed at the time, but there was a definite alpha-maleness about that, which I have never forgotten."

She backed calls for a "ministerial board" championing the economic benefits of gender diversity, but said companies must also explain why they have not signed a charter targeting female equality in financial services.

Mrs Gadhia said a move by City regulators to sign up to the Women in Finance charter had forced finance firms to confront the issue of gender equality.

More than 140 financial companies have signed up to the Women in Finance charter, which emerged off the back of her findings.

However, she said there were still prominent companies - including two investment banks - that had failed to put their names to the Government-backed charter, which links executive bonuses to gender diversity targets such as achieving a 50/50 split of women and men in senior roles.

The most controversial aspect of the charter has been the decision to link diversity targets to bonuses, Ms Gadhia said.

However, she defended the move, saying it provided a clear signal to boards that female equality was a business issue.