Directors Rupert Gowrley and Rachel Rowson, currently their deputies, will take over as interim joint heads of MHP Health Mandate immediately, reporting to chief executive Gavin Devine.
Birtwistle has been with the agency for 13 years and Winstone seven years. Both worked for Mandate before it merged with Hogarth and Penrose to form MHP in 2010.
Birtwistle is not moving to another job and has said he is currently focused on the transition with his future plans likely to be firmed up in September after he leaves. Winstone was not available for comment but an agency spokeswoman said she was understood to be in a similar position.
Both will continue to work with MHP Health Mandate on a limited number of projects until the end of the year.
‘The last thing I wanted to do was to leave clients I’ve got a good relationship with in the lurch,’ said Birtwistle.‘There are some things I want to see through to fruition so when MHP suggested that, I was happy to do it. ‘I’ll be doing that on a limited basis until December.‘I felt it was time for a change and I know Sarah (Winstone) had a separate but parallel thought process,’ he said.
Rowson stressed the departure was completely amicable.‘There will be a lot of continuity but this gives everyone an opportunity to rethink what we’re doing going into 2014,’ she said.