As others have said, it could be the gauge, a fuse or the sender unit.
Eddie51 is suggesting that it is unlikely that a fuse will supply power to the fuel gauge only – and therefore if it is a blown fuse, other electrical items will be non-functioning.
My bet would be the sender unit in the tank – but a garage would have to check all these things out. If I were a garage and had to replace a sender unit (which might involve getting the tank off), I’d want £100 including the part. And if it is a marque commanding premium prices for their parts (repaired at a main-dealer) you could easily double that £100 and then some.