Last year the amber oil warning light was coming on every 300 miles. Checked levels and topped up but oil always close to full. 

In November we had the sensor removed and cleaned. We also had the DSG oil replaced. 

All was fine until last week. Amber light came on. Topped oil (less than a quarter of a litre) 50 miles later, possibly less, light is back on. Checked the oil, its full. 

Going to be doing a couple of hundred miles next week as going on holiday. Obviously don't want to do any damage to the car.

Any advice? 

High oil consumption is common on the 1.8. Which engine do you have? There is a sticky thread above about 1.8 engine failures.

 

Alternatively your light is coming on due to low oil pressure. On high mileage cars be caused by a clogged oil strainer in the sump but almost always a diesel engine problem, not petrol.