MPs have criticised law firms for making "painfully slow" progress on gender diversity, in a report by the Business, Energy and Industrial Strategy Committee which calls for partners to be included in next year's pay gap reporting.

The report, released today (2 August) on the back of a parliamentary inquiry into the effectiveness of the first year of reporting, describes the exclusion of partners from last year's reporting as making "a nonsense" of efforts to tackle the pay gap.

Law firms and other LLPs were not required to include partner remuneration in their calculations as they are not technically employees, but the report calls for the government to make it compulsory for firms to include partners in the next round of reporting.

Smaller law firms and more US law firms with UK offices could also be included in the 2019 reporting, with the committee calling for last year's threshold for inclusion of 250 UK employees to be reduced to 50.

The report also issues renewed criticism of Allen & Overy's (A&O) handling of its gender pay gap reporting, after the firm refused to give up its partner figures when called upon to do so by the government earlier this year. A&O was the only magic circle firm that did not provide its 2016-17 partnership gender pay gap figures to the committee after it wrote to all five firms to request the data.

Today's report states: "We found it particularly surprising that Allen & Overy appeared unable to find a sensible way to publish, whilst others managed to do so." A&O plans to provide the select committee with a gender pay gap figure including partners for the 2017-18 financial year by September.

The committee also disparages the legal profession's efforts to improve diversity among its senior ranks, stating: "Whilst they pay lip service to their commitment to improving the representation of women… progress remains painfully slow."

It highlights Clifford Chance (CC) as an example of the lack of progress, noting that the firm – which has set a target of achieving a 30% female partnership – has seen an increase from 16.5% to only 21% since 2009.

The report states that it will take "many years" for legal firms to begin to "look anything like gender-balanced at the more senior levels", and urges firms to "redouble efforts to speed things up".

While acknowledging that there will be challenges to implement changes to the requirements in time for next year's reporting, the report calls "for the necessary amendments to made in one go, before the publication of the next round of statistics next year".

"Whilst this approach might limit comparability with the first year of data and require some swift consultation, there is benefit in establishing reliable figures which can hopefully form a consistent database for years to come," the report states.

Discussions over the inclusion of partners in pay gap reporting have already taken place, and this May, CC London managing partner Michael Bates and Pinsent Masons senior partner Richard Foley met with new Law Society president Christina Blacklaws to look at how to encourage more transparency next year.

In a statement, Law Society vice-president Simon Davis said: "The Law Society supports the inclusion of partner pay alongside employee pay data in gender pay gap reporting, to give solicitor firms a useful benchmark and enable an evidence-based action plan to tackle inequalities.

"We are working with the profession to develop a common set of standards that will provide the level of transparency expected by firms' clients, people and the public.

"Because partner pay is structured differently from salaries, a new reporting method will be required to ensure data is meaningful and helpful for addressing inequalities in pay. We will work with government and other professional and business services to develop an approach that is comparable across firms and industries."