Hi, 748rhydhir, There are two thing that caused be wrong with it,
1, the fuel gauge is faulty,
2, the fuel sender in the tank has gone faulty and needs changing,
3, there could be a wire come loose, or a wire broken on top of the sender,
many thanks for swift reply.apparently there was so little petrol in the car & she put so little in the sender had stuck down.her husband filled it right up & all is now ok