I've had my mk5 GT Tdi Sport since March and I've done 12k since, when I got it in March the low oil light came on a day later, no problem I thought, topped it up.
Did you not physically check the dipstick during your pre-purchase or pre-acceptance appraisal?
Personally, I would never touch a vehicle with a bargepole if I were to find the previous owner never dipped the oil and/or allowed the oil light to come on. The low oil light illuminating means that the engine is dangerously low on oil, and has obviously been neglected for a considerable period of time - and in my expert opinion, is a very BIG problem!
The only prob is I've had to top it up twice since, that's 3 litres in 12k.. is this excessive?
If you were to read your manual, you will find it is perfectly within tolerance. The VW limit for acceptable oil consumption is no more than 1 litre of oil per 1,000 miles - so yours is certainly within specs.
What could be causing this? How can I stop such an excessive consumption?
You can reduce your oil consumption by not waiting for the low oil light to come on. The lower the oil level, the more oil it will use. The best way is to go back to basics and check your oil level every week using the
dipstick. Topping up little and often is much better for engine life too.
It does smoke a bit under hard acceleration, which I was worried about, performance wise it's spot on,
What colour is the smoke?
Are you actually checking the oil and topping up
exactly as described in the owners handbook? Modern VW Group diesels must have their oil checked with the dipstick, and topped up when necessary, ONLY when the engine is at normal operating temperature - ie, HOT. If not, there is a very high chance of overfilling with engine oil when topping up.