2000 Vauxhall Astra smoke from exhaust and oil filler cap

What colour of smoke , white , blue ?

First thing to check would be oil and water levels .If it's white smoke , probably head gasket knackered . If it's blue smoke , usually indicates burning oil and engine probs , especially if back pressure through oil cap .

more than likey the breather pipe is blocked or folded in on its self check pipes for oil sludge which builds up in the pipes which also can rot the inside of the rubber pipes dont worry to much if its blocked this happens over time on most breather pipes most have a wire gauzes inside which trap the gue and become blocked

i agree with tony t here easy fix check for blockages and any weak soft pipes and replace them just for piece of mind