Employers should let women take career breaks of up to six years in order to build up their loyalty to the company, Dame Alison Carnwath, the only female FTSE 100 chairman, has suggested.

In an interview with the Financial Times, Dame Carnwath, who is chairman of property group Land Securities, says that companies exhibit ostrichlike behaviour about how much gender imbalances cost them. Instead, she suggests that if they accounted properly for the cost of recruiting and training staff who then leave when they start to find parenthood hard to juggle with working life, companies “would wake up to this much more quickly”.

To address this, shesays that employers should let women take career breaks of up to six years in order to build up their loyalty to the company.

In the interview Dame Carnwath also bemoaned the ongoing sexism in the banking sector, describing it as “very bad. On every score. Very bad”.

“The culture of some of these organisations means that females found quite a lot to cope with.”

In addition to her role at Land Securities, Dame Carnwath is also a non-executive director of insurer Zurich, private equity house Isis and US truck manufacturer Paccar. She is also a senior adviser to boutique banking firm Evercore and engaged in a pay dispute in 2012 when she was chairman of the bank's remuneration committee, arguing against the substantial pay and bonuses awarded to Bob Diamond, then chief executive.