those symptoms sound suspiciously like what went wrong with mine
have you checked the two fuel line connections on the top of the fuel tank??
lift he boot carpet and insulation and remove the round cover plate in the centre of the floor
under there you should find two pipes going into the top of the tank
mine had very badly corroded and were drawing air into the fuel lines
as a diagnosis, clean the area around the pipes if they look flakey, some paint thinners wiped round will get rid of any grease
then get some proper gooey mastic and coat the whole corroded metal part and leave it to go off
this will stop any air being drawn into the fuel. if it is that, either leave it till it reoccurs or you'll have to change the tank sender unit.
give it a whgirl as mastic costs pennies
