There is backlash in the party against the growing power wielded by union baron Len McCluskey (pictured)

It is being dubbed ‘Red Len’s political harem’ – a group of powerful women with close links to union baron Len McCluskey who are exerting an increasingly tight grip on the Labour Party.

But last night there was a backlash in the party against the growing power wielded by Unite’s Left-wing leader, with Corbyn’s critics calling it a ‘takeover by stealth’.

One senior source said: ‘We should hang up a sign in the office saying, “You don’t have to be close friends with Len to work here, but it helps.” ’

The row has blown up over the bitter contest to pick a new Labour general secretary – a hugely powerful figure who controls the party’s purse strings and membership – after moderate Iain McNicol quit.

Attention has focused on Mr McCluskey’s connections with three women who hold influential positions in Labour circles. They are:

Karie Murphy, Mr Corbyn’s Commons ‘gatekeeper’ who is also a close friend and confidante of Mr McCluskey. She is said to have played a key role in forcing out Mr McNicol;

Jennie Formby, Unite’s political director and a front-runner to succeed Mr McNicol. In 1991, Ms Formby gave birth to a child as a result of an affair with Mr McCluskey, who was married at the time;

Farah Sassoon, whose hotel booking business organises accommodation reservations for Labour’s annual conference. She is also in Mr McCluskey’s network of female Labour power-brokers. He was present at Monte Carlo’s luxury Hotel de Paris when she celebrated her birthday in 2016.

The growing influence of Mr McCluskey’s allies has led to friction with other senior Labour figures. Jon Lansman, leader of the Left-wing Momentum group that plotted Mr Corbyn’s rise to power, is determined to beat Ms Formby in the battle to become Labour general secretary.

The political careers of Ms Formby, Ms Murphy and Mr McCluskey are all closely intertwined.

Ms Formby was appointed by Mr McCluskey as Unite’s £75,000-a-year political director five years ago. Her promotion came after he was accused of trying to rig a Labour parliamentary selection contest in Scotland – for Ms Murphy.

Left: Farah Sassoon, whose hotel booking business organises accommodation reservations for Labour’s annual conference. Right: Karie Murphy, Mr Corbyn’s Commons ‘gatekeeper’ who is also a close friend and confidante of Mr McCluskey

Ms Murphy, who has been friends with Mr McCluskey for years, was forced to stand down as the Labour candidate in Falkirk over claims that Unite had cheated in the selection process.

She was later given a top job with Mr Corbyn at Westminster.

Ms Formby’s affair with Mr McCluskey was reported by The Mail on Sunday in 2013. We revealed official documents which showed that in 1991 she had given birth to a child by Mr McCluskey, who was married at the time and living in a union-subsidised home in London while his wife Ann stayed in his native Liverpool.

Jennie Formby, Unite’s political director and a front-runner to succeed Mr McNicol

Three years after Ms Formby had the child, Mr McCluskey divorced Ann. But instead of setting up home with Ms Formby, he moved another lover, Paula Lace, into his union-subsidised London home.

Ms Sassoon’s hotel and conference booking agency, Trust Reservations, is used extensively by the Labour Party. Two years ago, Ms Sassoon – who is best friends with Sally Bercow, the Commons Speaker’s Labour-supporting wife – invited Mr McCluskey to her birthday party in the billionaires’ playground of Monte Carlo. They were photographed together at the £1,600-a-night Hotel de Paris, which serves caviar and lobster sandwiches for £54, and charges £13 for a bottle of beer and up to £12,800 for bottles of wine.

Mr Corbyn’s critics say the growing influence of the inner circle of Mr McCluskey means he is gaining too much power over the party.

One insider said: ‘These women are all very formidable figures. McCluskey has more power over the Labour Party than Corbyn.’

According to some Labour sources, Mr McCluskey’s growing stranglehold over the party has caused friction with some Corbynistas, including some among Mr Lansman’s camp.

‘The hard Left has never seen eye to eye with old-fashioned trade unionists,’ said one. ‘It is increasingly impossible to do or say anything in the Labour Party now without worrying whether it is all going back to Len McCluskey. It does not help create an atmosphere of trust.’