Last night I'm leaving Sainsbury's, fuel gauge needle stays right at the bottom. On the way there I knew I was just about to go into the red and I'm sure I would have noticed a drastic leak...

Check the trip - miles until I run out of fuel is listed as "--". Fuel warning light was not illuminated. Was probably psychosomatic (sp?) but car felt slightly rougher than usual. Is it possible that if the car thinks you're gonna be out of gas imminently that it runs leaner somehow...?

Got back home, engine off, ignition back on, needle lifts, fuel light on and 45 miles until I need to fill up.

My car does have the occasional bout of insanity...

It's just to frighten you into going to a service station.