I think this could be the back-up battery wasted. As it is a old car I plan to disconnect the sounder.
Is it up behind the OS plastic wing splash guards ?.

Ian, May 2009

I believe it's under the bulkhead scuttle (the plastic cover the windscreen wipers come through) on the drivers side, assuming it's right hand drive.
To remove scuttle, remove wipers, then remove the 8 clips that are hidden under the rubber against windscreen. 1 screw in scuttle drivers side.
If the power sounder battery is failing it usually gives 4 beeps when you turn the ignition off.
Check the bonnet alarm switch as well.

futter, May 2009