>Without reverting to disruptive industrial actions, does anybody have any suggestions how to tackle this problem?<
Report 1 hour before as the company dictates and when you get to the aircraft do everything you need to do at a "normal" rate - if the a/c goes late and/or you miss the slot so be it! Trouble is most pilots don't want to start their duty day be departing late on the first sector.
In one company I flew with we had one Captain who reported exactly one hour before departure although most other crew members would be at least 15 mins early. On occasions he missed the slot but then surely flight safety and not expedition is the prime concern?
Not sure what CAP 371 says these days but there used to be a proviso that said that the Captain had the right to bring the report time forward if he/she deemed it appropriate.