I have been having a problem starting my car over the last few days and it is slightly spluttering when driving. Checked all the fuel lines and found air bubbles being drawn into the HP lucas pump

, so it is drawing in air from some where?. This is when i started getting confused and need help, when the ignition is turned on i was listening for the in tank fuel pump to run but no sound!. So lifted the back seat and removed the black cover, removed the pipe connections and plug, removed the locking ring and lifted out the....ITS only a fuel sender and NO pump.. I guess this is right

. So put it all back together and started checking the fuel pipe connections and fuel filter for leaks. The pipework looks ok but when i removed the fuel filter housing lid there is only a seal around the filter itself and not one around the housing lid?. This does not look right and when i refitted the housing lid and primed the bulb i can hear a slight hissing from around the lid edges, and more bubbles than before!!.
So does the 2.1td not have a lift pump and what seals should be in the fuel filter housing....