The number of women made up to partner at the UK's top 10 law firms fell by more than 25% this year, as law firms continue to struggle with the challenges of nurturing a strong pipeline of female legal talent.

An analysis of partner promotions at the UK's largest law firms reveals that while the overall number of lawyers making the grade across the top 30 has held steady, there has been a significant drop-off in the number of women being made up at the top end of the market.

At the 28 UK top 30 firms to have so far announced their 2016 partner promotions, 458 new partners have been made up. Of those, 147 (32%) are female – well down on 2015, when 173 women were made up in a total group of 454 new partners (38%).

The fall has been driven in large part by the UK top 10 firms, where 77 female lawyers were made up in 2016, down 26% from 104 last year. Eight of the top 10 firms made up fewer women this year than last, including Norton Rose Fulbright, which made up 12 female lawyers after promoting 19 last year, and Allen & Overy, which promoted six women after making up nine last year.

The picture is more positive outside of the top 10, with firms in the 11-30 bracket managing to hold female promotions broadly in line with 2015 levels.

DAC Beachcroft, Eversheds and Pinsent Masons were among a group of eight firms at which women comprised more than 40% of this year's new partners, while those to have significantly increased female promotions this year include Clyde & Co, which made up eight women compared with five last year, and BLP, where five of its new partners this year were female. The firm made up just one woman in 2015.

Managing partner Lisa Mayhew commented: "This really was an exceptional year but there wasn't a change in approach compared to previous years. We have stuck to what we always have done; promoting based on merit. We do have an ambitious gender target to reach 30% of women in our partnership by the end of 2018, but this year's cohort each provided a robust and ambitious business case."

The drop-off in female promotions comes despite the efforts of many top law firms to support the development of women on the partnership track. Bird & Bird, which has made up just two female lawyers in the past two years, recently announced plans for a new training programme aimed at boosting the number of women in its partnership.

Bird & Bird HR director Jonathan Nichols acknowledges the need to do more: "It's very much about promoting the individuals that are ready, but you can never guarantee it. We are hoping this year will be an anomaly."

According to many partners, the fluctuations in female promotions year-on-year lies in the lack of a sustainable pipeline at present, meaning efforts to increase the number of women one year can make it harder the next.

As Linklaters' managing partner Gideon Moore said in an interview earlier this year: "You need to look right at the beginning of the pipeline to see when the flow of women starts moving in the wrong direction…you need to work out and act where the problem starts."

Proportional representation

Looking beyond women to the promotion round more broadly, the firm in the number one spot in the revenue rankings, DLA Piper, made the greatest number of promotions in absolute terms this year, with 48. However, when expressed as a proportion of overall partnership size, a group of five firms emerge as the most generous promoters – Slaughter and May, Addleshaw Goddard, Eversheds, Macfarlanes and Berwin Leighton Paisner

Addleshaws' 15-strong promotions round this year equates to 9% of its total partner count as of May 2015, while Slaughters also boosted its partnership by 9%, with 11 promotions this year. Eversheds, Macfarlanes and Berwin Leighton Paisner (BLP) all added 8% to their partner count with their latest promotion rounds of 26, six and 17 respectively.

Capital gains

As has been the trend for several years now, international promotions outnumbered UK promotions by some margin. However, London this year gained a little ground with 32% of all of this year's new partners based in the City, up from 29% last year.

More than half of the 28 firms (15) made up more partners in London this year, with notable increases at firms including DLA Piper, which doubled City promotions from four last year to eight this year, and BLP, which made up 14 City partners after promoting just three in the capital last year.

Conversely, firms turning their focus away from London include Norton Rose Fulbright, where just two of 2016's intake of 39 new partners are based in the City; and CMS, which also made up just two in London this year and has now promoted just eight London lawyers in the past three years, from a total of 101 made up around the world.

The question now for many firms will be the extent to which Brexit affects future partner promotion rounds. While the UK's exit from the European Union is not expected to take effect until 2019 at the earliest, Brexit's immediate impact on the London market could well have a knock-on effect on career prospects far sooner. And for City lawyers on the partnership track, that business case could well become a lot harder to put together.