Mice will take over the world

I have already written about the Educated rodents and their efforts to eat my caravan. This week I found they had attacked my car too.
The Citroen had been running well since the Brakes broke episode. Okay it let me down a couple of times on cold mornings when the veg Oil heater knocked the stuffing out of the battery before it started, but it was nothign a jump start couldn't cure - and long term the cure was a new 63 amp battery to replace the 40 amp hour that comes as standard.
I decided to treat the car to an oil and filter change, and a new fuel filter at the same time. Oil change completed in an inpressive seven minutes. Now for the fuel filter - to get at it you need to remove the air filter box - not a problem, 1 x 10mm bolt, pull it out of the location pin socket and hey presto sorted. Okay, I leaked diesel all down my arm and all over the engine, but next time I'll know about the bleed screw on the bottom. And the process to bleed the system so the engine starts again when yo have the new filter on.
So what has this got to do with mice I hear you ask?
Well, after this unparralled mechanical attention the Citroen became extraordinarily difficult to start. The battery was going flat again, and the car was just coughing and refusing to run smoothly. Had I upset it?
Realising that a full servive probably involved replacing the air filter as well i removed the filter box and swapped the filter for a new one. Well swapped suggests an exchange of items like for like, which is strecthing the truth a little. The air filter that went in had rubber ends, a steel core and a paper filter element around the core. The one that came out had ..... fragments of paper, most of which had blocked the outlet preventing the engine from breathing. I an only guess at mice, although how theygot into the air filter box to eat the filter is beyond me. Given their enginuity in getting into my caravan I wouldn't put anything past the little bastards. They probably had rope ladders, and training bythe Mouse equivalent of the SAS.
Any way witha new filter the car is starting and running fine again. i just don;t know if I shoud install a rodent alarm and protection system