TD5 ABS current drain?

Hi Folks - my TD5 (auto & X plate) has an irritating habit of running its battery flat if I leave the car unattended for more than a few days. I've tried taking each fuse out to see which are still drawing current and rather oddly it seems to be the ABS that is the offender. As a comparison I did the same test on a friends TD5 (similar age) and his had no drain whatsoever. Why on earth would the ABS draw current when the ignition is off? I got round the problem when I left the car at an airport car park for a week by leaving the fuse out - but I would really like to sort it out. Anyone any bright ideas?