Fuel Gauge Problem

[foxy600]

Went out Sunday and while driving noticed my fuel gauge was showing full. I knew this wasn't the case so stopped and filled up. When I first started the car the gauge showed 3/4 full which was about right. then after driving again for 5 mins it showed full again!
I then stopped and switched off/on the ignition a number of times, each time the gauge only went down to half and after tapping it for a while finally went down to empty again.

Is this a simple case of a faulty gauge or could it be the sender playing up in the tank? Has anyone got any experience of removing this gauge as it seems impossible to get to?

[GreenV8S]

The sender is easy to get at in the nsr wheel arch so it would be possible to disconnect the gauge there, and measure the characteristics of the sender, and test the behaviour of the gauge when connected to the appropriate resistance. It does sound rather like a gauge fault given that it doesn't go to zero when you switch off, but it's possible there's something funny going on with the earths so not conclusive evidence of a gauge problem.