The drive to increase the number of female directors on the boards of Britain’s largest businesses is faltering – partly because of the unintended consequences of reforms that were supposed to increase boardroom diversity.

After several years of steady increases in the number of female-held directorships among FTSE-100 companies, the total has fallen this year according to an authoritative survey. And while five companies have appointed their first woman director, others have reverted to all-male line-ups.