Matrix Chambers is representing the National Union of Journalists (NUJ) in a group complaint relating to the BBC's gender pay gap, as it emerges that former BBC News China editor Carrie Gracie is among at least 10 senior female employees being advised by Mishcon de Reya.

The NUJ has instructed Matrix barrister Claire Darwin, who specialises in employment, discrimination and education, on a complaint on behalf of 121 female BBC employees over pay disparity between male and female workers.

The chambers joins Mishcon de Reya, which is advising a number of senior female BBC employees – including Gracie – on separate potential legal action relating to pay differences. Gracie has quit her role after four years and this week wrote an open letter citing a "secretive and illegal pay culture" at the broadcaster.

Mishcon employment partner Jennifer Millins is advising the group, which includes presenters named among the corporation's top earners in its annual report published this July. Employees are currently understood to be pursuing internal complaints with the corporation as a precursor to any later litigation.

Commenting on Gracie's resignation, Millins said: "The BBC may have hoped that its reported gender pay gap of 9.3%, around half the national average, would go some way to compensate for negative headlines it garnered on the issue last year. However, the BBC's gender pay gap figure is not an answer to individual equal pay complaints.

"As Carrie Gracie's resignation shows, failing to pay men and women who are doing the same work the same amount of pay can create a lack of trust between an organisation and its employees. Failing to deal promptly with internal grievances only serves to exacerbate this distrust, and in itself is a breach of an employer's obligations."

The report, published in July last year, revealed significant disparity in salaries for top male and female earners and prompted the BBC to appoint Eversheds Sutherland and PwC to carry out an audit of its pay structure. The audit did not deal with on-air presenters, editors and correspondents, whose pay is set to be examined in a separate review.

The report was overseen by retired Appeal Court judge Sir Patrick Elias QC and cleared the corporation of "systematic gender discrimination", but made a number of recommendations about how it could improve its practices.

Of the 96 individuals revealed in July's pay report to be earning more than £150,000, only 34 were women. Radio 2 presenter Chris Evans is the highest-paid man, taking home £2.2m-£2.25m – far outstripping the £450,000-£499,999 earned by the highest-paid woman, Strictly Come Dancing co-host Claudia Winkleman.

The report also included three of the BBC's in-house lawyers – group general counsel Sarah Jones, who earns between £200,000 and £249,999, and head of legal Peter Farrell and assistant general counsel Peter Ranyard, who are both paid between £150,000 and £199,999.

A BBC spokesperson said: "Fairness in pay is vital. A significant number of organisations have now published their gender pay figures showing that we are performing considerably better than many and are well below the national average. Alongside that, we have already conducted an independent judge led audit of pay for rank and file staff which showed "no systemic discrimination against women".  A separate report for on air staff will be published in the not too distant future."

The NUJ was contacted for comment, Matrix Chambers declined to comment.