Just to update, I topped the oil up to full with just over 500mls and the following day the warning appeared again. So I went to a BMW Dealer in Slovenia called BMW Avtoval d.o.o.. They had a quick look and said that it is the sensor that is on the way out. Obviously they couldn't replace it at such short notice but said fine to ride and replace when back in the UK. So I'll be doing that then as well as doing daily oil checks 