So I'm now sure its a Grohe Adagio cistern and I released the bracket and the bellows. It's not a pneumatic problem, so something to do with the discharge valve.
Concealed cistern. The push switch is a Herga, 4mm tube but I can't find anything on the Herga site. Fill valve is "the original torbeck". No idea if they would have been purchased together or separately.
Toilet will not flush. Maybe a leak somewhere in the pneumatics, or the flush mechanism is...