By Claire West

More than 50 company chairmen have joined the drive to improve the number of women on boards.

The influential bosses announced they are backing the 30% Club campaign for diversity in the same week that the number of women on FTSE 100 boards climbed to 16.7%.

Home Secretary and Minister for Women and Equalities Theresa May — who has led calls for change — joined celebrations last night as the 30% Club hit their half century.

She said: 'I'm delighted to help the 30% Club celebrate this significant milestone. The fact that over 50 chairmen are now supporting this initiative shows that diversity in the boardroom is increasingly becoming a mainstream idea.

'More women on a company's board is not just good for society; it's also good for that company's bottom line. An ever-growing number of businesses are realising this and — voluntarily — taking action.

'There is still a long way to go, but it's heartening to see the enthusiasm with which so many companies are embracing change and putting women at the heart of our economic future.'