Nigel Farage provoked controversy yesterday by claiming that women who take time off work to have children are "worth less" to City employers than men.

The Ukip leader made the comments during a speech in the City, arguing that women are able to do as well – if not better – than men but only if they are prepared to sacrifice family life. Farage argued there is no longer discrimination against women in financial institutions and suggested gender imbalances are caused by female employees making "different choices" for "biological reasons".

"In many, many cases, women make different choices in life to the ones that men make simply for biological reasons," he said. "If a woman has a client base and has a child and takes two or three years off work, she is worth far less to the employer when she comes back than when she goes away because her client base cannot be stuck rigidly to her.

"I don't believe that in the big banks and brokerage houses and Lloyds of London and everyone else in the City, I do not believe there is any discrimination against women at all. I think that young, able women who are prepared to sacrifice the family life and stick with their careers do as well, if not better, than men."

His views were immediately rejected by the Maternity Action group, which said it could make life more difficult for women returning to work, and Harriet Harman, the deputy Labour leader, who described his position as "absolute rubbish".

Rosalind Bragg, director of the charity Maternity Action, said she was "very disappointed at the criticism of working mothers".

"This will make life more difficult for the hundreds of thousands of women who are doing an effective job of balancing work and family responsibilities. We need practical support for new mothers at work, not more criticism."

Harman, Labour's deputy leader, said Farage's views about some mothers being worth less to employers were "downright wrong". She told Sky News: "To see a row of men sitting there and one of them saying that women are worth less to their employers than men are because they take time off to look after children I think is absolutely rubbish."There's not a single business or public service in this country which would still have the lights on if women weren't there at work. And yes, women do an important role in the home as well, not least because men don't share equally in the home and therefore it falls to women, but women are vital in their work and I think that that is an affront to women in this country, and I just can't believe that he's said that."

But Farage expanded on his comments in an interview on the BBC's World at One, saying there is "quite the reverse" of sexism against women in the City these days.

"I've noticed that the women that tend to get to the top and the women that tend to command the highest salaries tend to be women who haven't had families," he said.

"When I was an employer in the City, I would employ people in my brokerage company who I thought could bring in the maximum amount of commission business and people who have a lot of commission business to bring in, well, some can be lucky, but generally people who bring in commission business are people who've worked very closely with clients for years and years and years. If you have children and take nine months or a year, or maybe more off, you tend to lose some of that business.

"I think the reality for women in the City is that if they have children it has a very detrimental effect on their future pay prospects."

Asked whether this was fair, Farage said: "I can't change biology."

Meanwhile, Kirsty Ayre, a partner at law firm Pinsent Masons, said the notion that women are "somehow intrinsically worth less to financial institutions as a result of having families is laughable".

"These remarks reflect an incredibly narrow view of worth. The days when you evaluate someone's contribution based on their book of contacts are long gone and employers risk losing out on top talent if that is their attitude," she said.

Later, Farage was met by animal rights protesters and hit over the head by one as he visited Margate, Kent, near to the South Thanet seat where he could stand at the next election. Police had to intervene to protect the Ukip leader as he was mobbed by campaigners.