I had the same problem with a Rover 3500 I had recently bought. Unfortunately I discovered this 'foible' sitting on western road (when you could) at the Churchill Square traffic lights heading East.
Having to get a few buses and various other vehicles to back up so that me, my girlfriend at the...
It's worth remembering if you have a car that doesn't get run out that often (I have one that only gets used in the summer), petrol starts going off after about three to four weeks ???
But the others, normally somewhere between quarter tank and warning light.