As of June, 292 women held 339 directorships on FTSE 100 boards, of which a record high of 311 (38.9%) were non-executive directorships, according to Cranfield University.
Its latest Female FTSE Board report, supported by the Financial Reporting Council (FRC), also found that all FTSE 100 companies have at least one female director.
Meanwhile, 28 women hold executive roles in 25 companies, the majority of which (13) are CFOs or finance directors, while seven are CEOs.
However, the number of female chair positions decreased to five, while the number of senior independent directors rose only slightly to 21.
“There has clearly been great progress on the numbers front but scratch beneath the surface and we suggest that some companies have simply been ticking a box,” said Sue Vinnicombe, professor of women and leadership at Cranfield University.
She pointed to the “mounting evidence” of shorter tenures and the lower likelihood of women being appointed to senior roles.
The average tenure for male executive directors was double that of females – 6.6 compared to 3.3 years – with the gap slightly narrower for non-executive directors at five years and 3.8 years respectively.
The report found that female executives on average were younger than their male counterparts, and that this may point to mature women being overlooked.
“We need urgent action to make sure that women are being appointed to boards on and recognised for their contribution, and not simply for symbolic value,” Vinnicombe said.
Diversity at board level was also highlighted as a concern, with only 11% of women on FTSE 100 board being from Black, Asian, or Minority Ethnic backgrounds.
While 89.2% of the total number of women on FTSE 100 boards were white, only 5.7% were Asian, 2.3% black and 2.7% from other ethnic minority groups.
“Although it is positive to see more women on boards, we need to be sure that we are not only advancing progress for a certain group of women, but are truly pushing board diversity in every sense, said, Doyin Atewologun, director of the Gender, Leadership and inclusion Centre at Cranfield University.
In July, the latest Hampton-Alexander review found that the progress made by the FTSE 100 was not being matched by the FTSE 250.