What would cause the time and temp display to stay on on my 02 Astra?

I own a Vauxhall Astra 1.6 8v Club 02 and when I remove the key from the ignition the time and temp display stays on, sometimes the stereo stays on as well. Putting the key back in the ignition, several times, will sometimes cure this but most of the time not. This is an intermitant problem but has got worse lately. Sometimes, after an hour or so, the display will turn itself off. I wonder if a new ignition barrel would cure this problem? I'm sure you'll appreciate waking up to a flat battery in the mornings is more than a pain.