The UK boss of McDonald’s has told MPs that widespread cases of sexual harassment and bullying of workers at its fast food shops are “truly horrific” and that the chain was receiving one to two complaints a week about sexual harassment.

McDonald’s, which has 1,450 outlets and employs close to 180,000 people in the UK, most of them young people under 25, is under huge pressure to stamp out widespread sexual harassment and assault, racism and bullying, after an investigation by the BBC, which spoke to more than 100 current and recent McDonald’s workers, some as young as 17.

Alistair Macrow, the chief executive of McDonald’s UK & Ireland, told MPs on the Commons business and trade committee: “The cases are absolutely horrendous. What I’d like to be clear about is that we will tackle them and make sure that we do everything we can to eradicate them from the business. Nothing is more important.”

He said that, since July, McDonald’s had received 407 complaints “of all types”. Of those, 157 had been fully investigated and 75 had led to disciplinary action, including 18 dismissals. There were 17 confirmed cases of sexual harassment and 27 under investigation, as well as nine bullying cases and one related to racism. He said some had been reported to the police by individuals, but did not know how many.

Macrow told MPs: “To give you a picture of what we see on an ongoing basis, we typically would see between 20 and 25 contacts per week, of which one or two would be [about] sexual harassment. And about five would be bullying.”

He said there was no particular hotspot in the UK. “These cases come from across the whole business, including the restaurants we own ourselves,” he added.

McDonald’s uses a franchise system, which means outlets are run by individual operators who employ the staff. Nearly nine in 10 branches are run by franchisees. Macrow said no franchisees had lost their contracts as a result of the sexual harassment cases.

Macrow set up an investigations unit in late July after the allegations were revealed, and said then that the unit would refer the most serious cases to a third-party legal team staffed with “specialist investigators”.

The testimony from McDonald’s workers, some of which was read out at the committee hearing, was “truly horrific” and “very hard to listen [to]”, Macrow said, adding that some of the complaints stretched back as far as the 1980s.

Workers at McDonald’s have made complaints “in every shop” across London, according to the head of the Bakers, Food and Allied Workers’ Union.

Speaking to the committee earlier on Tuesday, Ian Hodson, the national president of the union, said it had received 1,000 complaints. He said they reported incidents of being groped, inappropriate language and treatment. “It was common and it was normal, which obviously it shouldn’t be,” Hodson said.

He said some of the stories were “absolutely horrific”. And it shouldn’t happen here in the 21st century in the UK. A global corporation, one of the biggest employers in the world, and that makes billions and billions of pounds, can’t protect its workforce. It’s awful. It’s awful. It should be leading and be an example for others. But they’re not.”

Last Thursday, the law firm Leigh Day launched legal action against McDonald’s on behalf of a group of the chain’s workers.