Yes, bookbinder is right. You may suck up bits of debris into the engine and you do not want that. I would say only about 35 miles on the red so you should fill up now. Motoring experts say you should always fill up before you get to the red so I would do that now if you can.
What happens when my wallet goes into the red? What do I do then?
Well I did make it home without stopping to put a fiver in at the expensive place. I thought about it but I'm put off by the girl that works in the garage. When she gives you change she sort of strokes your hand in a weird way. It's very off putting.
I rewarded the car by feeding it £30 of delicious petrol and will try harder to be a perfect car owner in future :)
If you re-read my answer I was not knocking you! only advising you on the Consequences of running short or getting very low on fuel, when I was on about Motorway's ( Again I was not knocking you) the distance now between Service Areas vary but should be 15 miles to each, if a car was to run out on the Motorway & in the outside lane this in-turn can cause someone to run up your @rse & even kill you, I was not preaching only advising.
50-60 miles, depends on your drive cycle and driving style, but you risk clogging up the fuel filter or worse, I don't normally let mine go below 1/4 tank.
Evian look in your car's manual. It will tell you how much petrol is left in the tank at the point the warning light comes on. You can then work out how far you can go before running out.