Ms Villalba was made redundant last August

She also said the bank's male-dominated management culture boxed women into a vicious circle of poorer pay.

Merrill Lynch denies the allegations, and says Ms Villalba was dismissed for making "record losses".

If she wins the unfair dismissal case, the damages could be the biggest awarded by a UK employment tribunal.

Ausaf Abbas clearly bullied, belittled, undermined and underpaid me. Stephanie Villalba

It is the latest gender bias claim facing US bank Merrill Lynch. The bank has already paid $100m (�53m) to settle nearly 900 claims in recent years.

Last month, it settled a 10-year battle with 1,000 female workers in the US who had claimed that the bank had a culture of bias against women.

And in April, the investment bank was ordered to pay $2.2m (�1.2m) in damages to Hydie Sumner, a female broker at its San Antonio, Texas office.

Made redundant

Based in London's financial district, Ms Villalba worked for the bank's global private client business in Europe, investing funds for some of Merrill's most important customers.

But last August her employers told her she had no future in the company and she was made redundant.

We are disappointed that Stephanie has reacted by attacking the character of one our most respected managers who has been with us for 20 years and has an outstanding record. Merrill Lynch

The tribunal has already been told that while on a trip abroad in a corporate jet with colleagues, Ms Villalba's male boss - Ausaf Abbas - told her to sit where the cabin crew sat and to serve drinks to the six male colleagues present.

"Ausaf Abbas clearly bullied, belittled, undermined and underpaid me," Ms Villalba told the tribunal.

"He poisoned others against me and successfully stigmatised me as a problem and a liability."

Mr Abbas is also alleged to have described Ms Villalba as "high maintenance", and once when Ms Villalba said how hard she worked, he is said to have replied, "Stephanie, my maid works hard".

Merrill Lynch denies Ms Villalba's claim and says she was removed from her post as head of the company's private client business in Europe because of the extensive losses the firm was suffering on the continent.

Nicholas Underhill, acting for Merrill, said it is "simply not the case" that Mr Abbas made the comments on the plane and that the term "high maintenance" was not gender specific.

Executive witnesses

Mr Underhill said the maid comment was only meant to mean that "working hard is not enough".

He added that the decision to replace Ms Villalba was "a judgement based on her performance at that time, it was nothing to do with sex".

The "evidence is overwhelming that she was doing badly" in this role, he added.

"This whole case boils down to one issue - performance. She was given a major business within the firm to run - and she wasn't successful," Merrill Lynch said in a statement.

"She was replaced by another woman who has helped turn around the business and is doing very well. Stephanie was offered other positions within the firm, all of which she turned down.

"This isn't a realistic claim. We are disappointed that Stephanie has reacted by attacking the character of one our most respected managers who has been with us for 20 years and has an outstanding record."

This case, which is scheduled to last for 30 days, could be particularly damaging to the investment bank as it threatens to uncover the US bank's most sensitive inner workings.

High-ranking Merrill Lynch executives are on standby to fly from New York to defend the bank at the tribunal in West Croydon.

They are likely to include Mrs Villalba's immediate boss, managing director Phil Sieg and his senior Raymundo Yu.