Adrian Sutil
Membership of GPDA is not compulsory. For example, during the 2013 Formula One season, only 19 out of 22 active drivers were members (with Kimi Räikkönen, Adrian Sutil and Valtteri Bottas being the exceptions). Joining the GPDA costs £2,000. It was announced on 13 December 2017 that all the drivers had signed up.