Dodgy fuel gauge ?...or something else

Just got myself a 2003(53) disco and loving it...however....it appears the fuel gauge is dodgy to say the least. When I fill it up, the needle goes a little past the "full mark" , however, the tank then appears empty when the needle falls to just below the quarter tank mark. After contacting the dealer and explaining the symptoms, ie Disco will not start and makes a strange noise from rear near side, I was told that it must be the pump trying to pump fuel that was not there. In other words, put some diesel in and try again. I did this and she started. Left it running for a fair few miles and she cut out again - once more this was when the needle fell just below the quarter tank mark. Please help - the dealer reckons it is the sender unit and has one on order for me but my fear is that he is trying to pull a fast one. Any ideas/advice would be most welcome

The sender unit is part of the fuel pump in the tank. The cheap ones last 12 months but cost £150, the Genuine ones are 220ish. VDO supplied units are OEM/Genuine spec.

get a new pump which will have good sender too... IMO that will cure everything

when it cuts out, fill the tank all the way up and see how many liters. that way you'll know if its the sender or a tank full of crap in the bottom.