It has a fault & you have now gone 50% of the way to it being a deadly one. There is power leaking to earth. All that needs to happen now is for the earth to get a fault & the case will be live just waiting for you or some other unlucky bugger to touch it.
Without RCD one fault can be safe, two faults are deadly. With RCD the first fault trips it.
what they said plus
the best thing to do is to get the supply side folk to check their lines/tranny/earths etc and for you to get a good spark to test your lines and equipment.
your tests should not cost more than a couple of hundred quid tops but will potentially save bother,freezer contents and possibly life.
first thing you can do is a visual assessment for anything obvious,wet stuff ,scorch marks,branches,(old uncle fred's 1930's toaster etc etc )
Thanks guys. All has been fine for the last 24 hours so suspect the wet weather might have been to blame but getting a sparky to do an inspection has to be the next step..
We've already lost freezer contents during a couple of summer holidays in the past (as our neightbours have done) so i am guessing that it is partly to do with where we are and the wet conditions but would be better to check it out in case there is something amiss as well.