Iv just brought a 51 plate KA standard model. The fuel gauge is on half weather the engine is running or not. Iv put £10 of petrol in and it shot to full and after doing about 5miles it's back on half. Does anyone know what could be causing this?? How much it would cost to fix?? Typical women so it's Defo a garage job. Also mot due soon, would this effect it?? (sorry if that's a silly question :-))

It's either the guage is sticking or the fuel level sender in the tank.
It's probably easier to check/change the guage first.
To check the sender you would need access to the top of the fuel tank.

Thank you. Do you know how i would check it? Or the costing for getting a garage to do it?