A couple of months before Christmas, invitations began landing on the leather-topped desks of some of London's most powerful businessmen.

Embossed, and carrying a quasi-masonic logo based on an italicised letter P, they encouraged wealthy recipients to spend £2,000 a head bringing friends and contacts to an event at The Dorchester hotel.

Called the Presidents Club Charity Dinner, and held each January for the past 33 years, the lavish bash has, in certain rarefied circles of the property and finance industries, become a staple of the social calendar.

Footage: Hostesses in black dresses mingle with guests at the Dorchester charity gala

Like many a black-tie fundraiser, its format is simple: Guests get a chance to network with fellow high-rollers – as well as a smattering of willing celebrities – while dining on fine food and wine and giving millions of pounds for good causes in the process. Every year, a famous entertainer or two will perform.

Someone well-known will deliver a knockabout after-dinner speech. Then well-refreshed punters will be invited to unfurl their chequebooks and bid huge sums for a selection of high-end luxury products, fast cars, holidays, and various money-can't-buy special lots in a turbo-charged charity auction. Afterwards, there's a disco.

In these enlightened times there is, however, one very unusual feature of every Presidents Club dinner.

In order to attend, you are, without exception, required to be a man.

What's more, organisers have come up with a cunning way to replace the wives and girlfriends who would usually provide what's colloquially known as 'arm candy'. It involves many attractive young women being paid to join punters at their tables as 'hostesses'. Their role is to talk, entertain and, if necessary as the evening progresses, dance with the generally middle-aged men.

Thousands sign workplace harassment petition in wake of Presidents Club scandal More than 50,000 people have signed a petition set up in the wake of the Presidents Club scandal calling for more protection from sexual harassment in the workplace. The Change.org campaign was started on Wednesday after allegations surfaced that hostesses were groped at the Presidents Club's men-only annual fundraiser. The petition calls for the reinstatement of Section 40 of the Equality Act, which made employers liable for an employee being harassed by a third party - such as a customer - if the employer did not take reasonable steps to prevent it. The section was repealed in 2013. The woman who set up the petition claimed to have been a victim of inappropriate behaviour at work, and said she wanted to stop organisations 'turning a blind eye' to the issue. Advertisement

This strange and somewhat seedy arrangement has for years been the source of much nudging and winking in the City of London.

It also helps explain why – despite its starry guest list – the Presidents Club has chosen to keep its annual shindig firmly below the radar.

Photographers are banned, mobile phones are confiscated from staff who work there, and the names of patrons have always remained a closely guarded secret. Until now, that is.

Last Thursday, at least two of the 130 young female hostesses paid £150 (plus a £25 taxi allowance) to spend the evening at The Dorchester with 360-odd male revellers were not entirely as they seemed.

Rather than being aspiring models and actresses, or hard-up students earning some extra pocket money, they were undercover reporters working for the Financial Times.

Details of what unfolded at the event, which ran from 8pm to 2am, were published yesterday – and have sent shockwaves through the worlds of business and politics, not to mention the charity sector.

Put bluntly, it seems that a hefty proportion of the women working at the Presidents Club dinner – which was compered by comedian David Walliams and attended by senior representatives of a host of blue- chip City firms, including the advertising agency WPP, Barclays bank and the property giant Residential Land, which is run by Presidents Club co-chairman Bruce Ritchie – found themselves being groped, sexually harassed and lewdly propositioned.

Some of their alleged abusers were captains of industry and household names.

Some were repeatedly fondled as they attempted to tuck into their meal of hors d'oeuvres, smoked salmon with caviar and beef aged for 40 days.

Others complained that some of the men in attendance had grabbed their bottoms, hips, stomach and legs. One shell-shocked 19-year-old hostess was asked by an elderly man if she worked as a prostitute.

'I've never done this before, and I'm never doing it again,' she said. 'It's f*****g scary.'

As the evening wound on, one guest lunged to kiss the FT's undercover reporter. Another invited her upstairs to his room. She later heard one young woman complain that the man sitting at her table had exposed his penis to her.

After dinner, guests adjourned to an after-party where an unnamed society figure was observed confronting at least one hostess directly. 'You look far too sober,' he announced, filling her glass with champagne before grabbing her by the waist and declaring: 'I want you to down that glass, rip off your knickers, and dance on that table.'

Attractive young women are paid to join punters at their tables as 'hostesses'. Pictured: Footage from the event this year

In the centre of the room, Jimmy Lahoud, a 67-year-old Lebanese businessman and restaurateur, was, according to the FT, dancing 'enthusiastically with three young women'.

'I was groped several times and I know that numerous other hostesses said similar had happened to them,' the undercover reporter, Madison Marriage, recalled.

'It's hands on bums, hands up skirts, but also hands on hips, hands on stomachs, arms going round your waist unexpectedly. One of the strangest things was you could be talking to a man and he'd suddenly start holding your hand.'

Scandalously, these unedifying scenes appear to have occurred not by accident, but by design. Artista, a Berkshire events company, was hired to source the 130 hostesses for the evening. It claims on its website to work for a number of major firms, including Bentley, Aberdeen Asset Management, Moet Hennessy, the Economist, and, oddly, the Royal Windsor Horse Show.

Guest: Tory MP Nadhim Zahawi

Hostesses were selected for being 'tall, thin, and pretty', and told to wear 'black sexy shoes', black underwear, and the sort of make-up they might choose if going to a 'smart sexy place', the FT reported.

They were expected to drink alcohol, but warned that men in attendance might try to get them 'p****d'. Their phones were confiscated and they were required to sign a five-page non-disclosure agreement banning them from talking later about the proceedings. 'It's a Marmite job. Some girls love it and for other girls it's the worst job of their life and they will never do it again,' Caroline Dandridge, the founder of Artista, is said to have told one hostess.

'You just have to put up with the annoying men, and if you can do that it's fine.'

It appears that the sexualisation of the Presidents Club event was used as a fundraising tool.

Hostesses were introduced to guests by being paraded across a stage to the song Power by the girl band Little Mix. As they walked to tables, pictures of sick children were flashed up on video screens.

At dinner, a troupe of burlesque dancers performed while dressed as Coldstream Guards, wearing star-shaped stickers to hide their nipples.

It appears that the sexualisation of the Presidents Club event was used as a fundraising tool. Pictured: Attendees at the event

Lots sold during the fundraising auction included a night at Soho's Windmill Club – a lap-dancing venue whose licence was revoked recently after dancers were caught flouting no-touching rules, and a course of plastic surgery that was promised to 'add spice to your wife'. The auctioneer was filmed drumming up bids by announcing: 'This is what your Missus could look like! Who'll give me £10,000?'

Perhaps understandably, a number of guests who attended the event rushed to disassociate themselves yesterday from any allegations of impropriety.

Mr Walliams, who had compered the event for the third year running, declared himself 'absolutely appalled' and said he left early and did not witness any wrongdoing.

Tory junior minister Nadhim Zahawi claimed to have been unaware of the nature of the bash when he accepted the invitation (although the BBC has reported that it was his second time there, having also attended before he became an MP).

Others caught in the fallout, having been in the room, include Ocado founder Tim Steiner, clothing tycoon Sir Philip Green and Dragons' Den star Peter Jones. His former colleague on the show Theo Paphitis also featured on the guest list, although it's unclear whether they actually attended.

Bruce Ritchie and wife Shadi

There is no suggestion, though, that any of them were involved in any inappropriate behaviour. With Great Ormond Street Hospital having pledged to give back money raised by the Presidents Club, there are also awkward questions to be asked of the scores of other charities to have received funds.

They range from Prince Charles's Prince's Trust to such blue-chip outfits as the Tate Gallery, Cancer Research UK, the British Olympic Association, the NSPCC, the Lord's Taverners, and the scandal-hit and defunct Kids Company.

In defence of those involved, it should, of course, be pointed out that the main aim of the Presidents Club is to raise money for good causes. Last Thursday's event generated £2 million.

One well-known attendee, who spoke to the Mail on condition of anonymity, claimed he saw 'nothing worse than what would happen in any nightclub in London any night of the week,' and said it was 'tragic' that 'political correctness means money will no longer go to dying children'.

But they can't say they weren't warned. As long ago as 2004, when the then London mayor Ken Livingstone was the guest of honour, newspaper diary items remarked on the 'large numbers of very pretty women in attendance'.

Four years later, when the guest list was said to have included Formula 1 tycoons Bernie Ecclestone and Flavio Briatore (who was once chairman of Queens Park Rangers), property developers Nick Candy, David Reuben and Gerald Ronson, and comedian Jimmy Tarbuck, a report drew attention to the large number of hostesses paid £120 for 'fetching drinks' and 'socialising with' the glitzy guests.

'It was quite a racy event... but the beauty parade seemed to be something of a hit,' the Daily Telegraph noted. 'The boys tucked into the girls.'

But now it has ended in tears.