Forum topic: bad oil leak need advice

I have a defender 110 200tdi that is leaking oil from the top of the engine [cover or head gasket area], now when i start it up there is white smoke, when i first start to drive it with engine cold it is fine, but when the temp guage goes up and the engine gets hot[roughly after 25 minutes or so] and i go to accelerate it is very very sluggish, very low power , if there is a leak in a gasket somewhere will this cause compression loss? a friend thought he saw bubbles coming out of the gasket area. I hope someone can answer my questions please. Is it wise to continue driving the vehicle or am i just loosing oil? any free answers are great education for me as i am a rover newbie too. thanx gang.

jeff b