Help - Xenon lights slow to switch on
 

I wonder if anyone can help at all, when I switch on my xenons there is a delay (anywhere from a few seconds to several minutes) before the lights actually come on. This is happening to both the headlights, and when they come on they do so at exactly the same time.

Once the lights have been on a little while I can switch them off and back on again, at which point they will fire up instantly as they used to.

This has now been happening for about a week and is the same every day.

Any ideas ? Any help will be greatly appreciated.

Paul