Why is my Audi A4 2010 petrol only doing about 300 miles before oil light comes on

The common problem here can be a dirty airfilter which requires the engine to go heavy and get more power from engine. Change it alongside oil change and be sure to change oil after 100 miles

2 questions.
1) Is the oil actually low on the dipstick?
If it is, you might have an oil leak, so you would need to look underneath and see. Also look for puddles when you park.
The most common reason for such consumption would be a burst oil pressure switch, or a leaking valve cover gasket.
Either of these will leak lots of oil.
The last possible reasons, which are really rare, would be engine parts defective,( like oil rings), or a leak in the brake booster which would suck oil from the crankcase into the brake booster.
2) If the oil is not leaking out, and the dipstick shows full, you will be needing a new oil pressure switch, or to have the electronics repaired.
God bless your efforts.