I planned my return trip abroad the previous afternoon, filing my outbound and inbound fpl and inbound GAR. I got confirmation email of all three all correctly showing my date of flight as the next day.

Later that afternoon i got a call from Borderforce , they have been informed by the "CATS" system whatever that is that my dof is today not tomorrow and they want to know why theres no GAR filed, although the do have one for the next day.

This is the second time this has happened, anyone else had this and how to avoid it happenning again?

Borderforce went to the trouble of checking with my FBO the my aircraft was safely tucked up in its hangar and not in Holland as the CATS system thought.

Neither we nor the people behind the online GAR filing system have ever heard of a "CATS" system. There is certainly no such system forming part of the current GAR requirement.