“When presenting their long lists, search firms should ensure that at least 30 per cent of the candidates are women — and, if not, should explicitly justify to the client why they are convinced there are no other qualified female options,” according to the voluntary guidelines announced on Friday by the Department for Business, Innovation and Skills in London.

Nineteen leading headhunting firms have pledged to sign up to the code for future boardroom appointments, the BIS said. Among the signatories are Korn/Ferry Whitehead Mann, the UK arm of Korn/Ferry International.

A panel led by Mervyn Davies, the ex-chairman of Standard Chartered Plc, recommended in February that companies in the UK’s benchmark FTSE 100 index should double the proportion of women on their boards to 25 per cent. It said shareholders should hold companies to account if they fail to appoint more women.

“This code is a positive step forward and I hope to see all executive-search firms signing up to its recommendations,” he said. Implementation of the guidelines will mean “the headhunter community will help to bring more talented women to the top table, improving board effectiveness in the UK.”

A study of FTSE 100 company boards published in December by Cranfield University School of Management showed the proportion of women at senior levels in firms was 12.5 per cent. Eighteen of those companies have no female directors, Davies said in February. Headhunters should explore with company chairmen whether recruiting female directors is a priority in specific instances and should also provide support to first-time candidates to prepare them for interviews, according to the code.