Turns out that when the car was serviced before I bought it about 3 months ago, they used a wrench to tighten the oil filter and put a tiny hole in it. Whist driving the oil was slowly leaking out and hey presto....it pretty much ran out. Hence the smoke yesterday and today. New filter and 5ltrs of oil later from STechnic and I'm all good again. No rattles on start up so he's fairly confident there's no damage.