In February, former trade minister Lord Mervyn Davies of Abersoch carried out an independent review, Women on Boards, which recommended that chairmen of FTSE 350 companies set goals for increasing the proportion of women in the boardrooms by September. He suggested a minimum figure of 25 percent.

In the letter to company chairmen, Cable and May said that there was a "strong business case" for increasing the proportion of women on boards.

"Inclusive and diverse boards are much more likely to be better boards, better able to understand their customers and stakeholders and benefit from fresh perspectives, new ideas, vigorous challenge and broad experience, which in turn lead to better decision-making," they wrote.

Some progress has been made since the report, Cable and May said, particularly among companies in the FTSE 100.

The number of all-male FTSE 100 boards fell from 21 in October 2010 to 14 this month, and in addition, they said that the rate at which women have been appointed to board positions has "significantly increased".