Update ! Spoke to my mate last night who is a triumph technician .
He says that he has seen this problem in a few rockets where the gear lever return spring has lost its tension . Not due to breakage but more down to the quality of the spring used in some bikes causing it to become slack !
Not a huge issue at present , but when all tension is lost the weight of the gear lever and linkage can overcome the detent spring on road bumps and cause the bike to jump out of gear .
So , new spring , circlip and cover gasket on order !