The former chief executive of Britain’s largest gay rights charity claims to have heard of “dozens of cases from men and women” of alleged sexual harassment at Westminster.

Channel 4 News revealed in a survey of 70 people from across the political spectrum, one in three had experienced sexual harassment, and men are more likely to be victims.

Twenty one percent of people surveyed had witnessed or heard someone else being sexually harassed. Less than half (46%) said they had no second hand knowledge of such behaviour. And 40% of men surveyed had received unwanted sexual advances.

Channel 4 News published the results in an investigation named ‘The Palace of Sexminster’ last night – on the same day MP Nigel Evans was cleared of all rape and sexual assault charges.

Former Stonewall CEO Ben Summerskill, also described as a political lobbyist, told Channel 4 News: “Sexual harassment is part of the culture of Westminster. In the last decade I’ve heard of dozens of cases from men and women … people are vulnerable as they’re often political obsessives and have never worked anywhere else.”

“For both sexes the MP can say that if they oblige them, it might help their career enormously. There’s no HR, no structure for people management or supervision,” he said.

Ben Summerskill resigned as chief executive of Stonewall in February. He had been at the charity for 11 years.