Astra "51" reg - cust out when warm, restarts when cold.

I have a simple and persistent problem with my Astra. I can drive it for about 10 to 15 minutes - nice and smooth - then it just cuts out and it wont restart until it cools down - maybe around 20 minutes later. Is there some kind of temperature safety cut-out on the astra that may be malfunctioning. obviously after only 10 minutes it's not execessively hot. Is there some kind of fan-failure cut-out that cuts the engine out if the cooling fan will not come on? Tom