The exploitation of vulnerable young parliamentary researchers by predatory MPs is being "brushed under the carpet" by the main political parties, one of the alleged victims of Nigel Evans has claimed.

The former deputy speaker was yesterday cleared of a string of alleged sex offences - including one allegation of rape - by a jury at Preston Crown Court.

But one of the men he was alleged to have assaulted has accused the parliamentary authorities of ignoring a problem that was widespread at Westminster.

"I don't think any of the main parties know what to do. The strange (thing) about Parliament is that they make the laws but they don't act like any other place of business," the man, who has not been named, told BBC2's Newsnight.

"Researchers and MPs' staff don't even have a HR department. Our bosses are technically self-employed. Even though we work in one big building together there was no mechanism to deal with this problem. There still isn't.

"They (the parties) were certainly aware that there are MPs and young, 20-something researchers who are vulnerable because they fear for their careers and all the hard work that they do could just be thrown away in an instant. I think that a lot of senior people count on that - that it can be brushed under the carpet.

"There are some young researchers who simply enjoy the contact - that's entirely up to them. But there are plenty, if not most, who don't appreciate that at all. They just want to work. They got into politics because they want to change the world but they find that when they get there they've got to put up with a lot of stuff."

The man said that he was "really angry" at the verdict, describing his experience in the witness box as "difficult and degrading". He said that the case had destroyed his hopes of building a political career of his own.

"I've lost everything in this last year and had to slowly rebuild my life. I had ambitions for a political career. I don't see that as a real possibility any more."

But another alleged victim in the trial told ITV news after the verdict that he didn't think Mr Evans should have been charged, the Guardian said.

The man said: "I don't think it was a criminal act. it's the sort of thing that happens in every bar. It wasn't a big deal."

Other young parliamentary workers have described a culture where MPs regularly drink with staff in the building, creating the possibility of compromising situations.

One of the witnesses in the Evans case, who said he did not see himself as the victim of a criminal act, told The Independent there could be a "curfew" in parliamentary bars to reduce the possibility of inappropriate behaviour.

He told the newspaper: "MPs are working away from home for three or four days at a time. You add to that the late nights, the drinks, the general sense of power and you can easily see a lot of people crossing over that line."

Another parliamentary worker in his 20s told the newspaper that a group of Tory MPs would drink with other staff, and they would be drunk, "flirting with us and sometimes more... no one batted an eyelid".

The man suggested there was "complicity" on both sides and it was not solely a case of MPs taking advantage of younger staff.