Cooke led the Theodores negotiations with Salans last year, which eventually collapsed in September.
He has worked closely with fellow employment partner Bullen, who took over at the helm of the employment practice when Cooke became managing partner in 1999.
The Lawyer understands both were proponents of a Salans tie-up and were disappointed when it fell through.
There have now been 10 departures since the Salans talks failed, four from employment. Earlier this year empl-oyment partners John Evans and Mark Catchpole left for Coudert Brothers and Steph-enson Harwood respectively.
Theodores now has just one partner in employment and around 10 fee-earners.
Theodores managing partner Nigel West said the firm had not decided whether to look internally or externally for a new head of employment. One source said the employment department has had a particularly high turnover, although West denied that this was the case.
The move is a significant coup for Salans and will double the number of partners in the UK employment team, which is headed by Barry Mordsley.
A Salans source confirmed the move but did not wish to comment further at this stage.