battery drain

hi guys, i have the dreaded battery drain, i have a 2007 s type xs 2.7d, its been fine for the eleven months ive owned the vehicle, but suddenly the battery was flat when i went to use the car, charged battery and started fine, left outside locked and armed that night and dead in the morning, thought the battey may have dead cell so purchased a new batterry which was fitted to the car fully charged and was dead within two hours!!!  when i say dead i mean absolutely dead, nothing, no lights no ignition lights no power anywhere, had all electrics checked, all fuses pulled and monitored, and diagnostics plugged in and checked with nothing found, i now have to disconnect the battery after use, ( used every day) i forgot to disconnect yesterday, went out to disconnect an hour later but it was to late, it had drained the battery totaly, ive watched to see if anything becomes live after ive left it but nothing being reactivated that i can see, i am at a total loss  as to what is going on as is the electricians, can anyone shed any light on this?