This has been a problem affecting mainly older vehicles with steel fuel tanks, the water in the fuel rusts the inside of the tank over a period of time, the rust eventually flakes off and blocks pickup pipes/filters. The water tends to be in the supply from the pump particularly from filling stations that are not mainstream, this has become less of a problem as smaller 'corner' garages become less and less. Keeping the fuel tank contents low can cause condensation on the walls of the tank, this eventually finds it's way to the bottom of the tank as diesel floats on top of the water. Another way of adding contamination is from fuel containers used during off road activities, to help with this and with regards to the 80 diesels there are THREE filters, the first is on the pickup pipe and this has been known to restrict fuel, second is the familiar large filter under the bonnet, and there is a third with a very fine mesh at the fuel pump inlet solenoid. My experience is that the pump filter is not normally contaminated, the first two however have often been seen to be blocked or at least severely contaminated.
regards
Dave