Almost a third of Olswang's partnership left the firm in the financial year before its merger with CMS and Nabarro, Companies House records show.

In total, 28 partners departed between 1 May 2016 and 30 April 2017, equating to 28% of the firm's total partnership, based on its 2015-16 partner count of 101.

Eleven of the exits were from Olswang's London headquarters, while the other 17 were from the firm's offices in Paris, Germany and Singapore.

Olswang's three-way merger with CMS and Nabarro went live on 1 May this year, after partners voted in favour of the deal last October.

Key London departures in the 12 months prior to the merger's completion included intellectual property (IP) partner and co-head of life sciences Stephen Reese, who joined Clifford Chance, former interim CEO and IP partner Michael Burdon, who joined Simmons & Simmons, and patent prosecution group co-chair Justin Hill, who is now at Dentons.

Ahead of the tie-up, Olswang closed its offices in Paris, Madrid and Brussels. Paris managing partner and corporate head Guillaume Kessler joined Orrick Herrington & Sutcliffe, while local employment partner Karine Audouze left to launch a base in the French capital for US firm Ogletree Deakins.

The sole partner in the Madrid base, Blanca Escribano, stayed with the merged firm and now heads the digital and data group at CMS Spain in Madrid.  All six lawyers in Olswang's Brussels office joined CMS's local arm.

Meanwhile, the five partners in Olswang's Munich office all found new homes, including patent litigator Thomas Lynker, who launched an IP, tech and media boutique with a group of colleagues.

In Singapore, technology partner and former Asia head Rob Bratby quit for Arnold & Porter's London office.

A CMS spokesperson said: "To give some context, a number of these departures took place well before merger discussions began and bear no relevance to the current firm.

"As to be expected with a combination of our size, there were a small number of partners that were not able to accept offers as a result of conflicts or other issues. Looking forward, the combined firm is in a strong position and we are continuing to make the most of the opportunities that the merger presents."

Legacy Olswang and Nabarro partners who stayed with the merged firm signed a lock-in agreement which commits them to CMS until May 2018, although partners who were at CMS prior to the merger are not subject to the same restrictions.

CMS recently posted a 1% dip in global revenue for 2016, after taking in €999m during the calendar year. The full contribution of the Nabarro and Olswang mergers will be revealed next year, when global revenues are expected to surpass €1.2bn.