1998 Vauxhall Sintra excessive smoking

I have just bought my Sintra and being plaqued by the usual electrical problems. Windows not working adn the speedo works intermittantly. However what worries me is the exessive white smoke from the exhaust. When I first start the car there is hardly any smoke but after a couple of minutes it starts to emit lots of whiteish smoke, it doesn't seem to be burning oil but it does smell of petrol and chokes everybody stood near the car. I know it's been cold and damp lately but the smoke doesn't seem to stop once the car has been on a run even. It doesn't have a sweet smell and I've checked the oil filler cap and there is no trace of an head casket gone as there doesn't seem to be any creamy colour in the cap and it just seems to be fresh oil. The exhaust does sound like it does have a leak when I rev the car although I've been assured by the MOT station that passed it that there is no leak, although they didn't rev the engine when they checked it over. So wonder if this could be a catalytic converter problem or worse. The car is under warranty so wanting to check this out. I hope this seems ok as it is a biggish engine at 2200cc so perhaps this could be normal or so the salesman tells me. He told me that he will mend the speedo but he says it's something to do with the sender on the gearbox but I suspect from what I have read that it's more to do with the sensors on the front hub as there is no ABS light that should come on with the ignition.
Thankyou for any help with this as although I like the look of this car and the room. The car pulls and runs well and with no misfiring at all.
Best regards
Graham