The TD5 engines use Lucas Delphi injectors which operate at a collossal pressure, about 1,500 BAR, more than TEN TIMES a normal Landy Injector. The fuel returned from the injectors is VERY VERY HOT, and spills back into the fuel gallery in the cylinder head, which will be about 90°C during normal running.
The fuel return line passes through a heat-exchanger COOLER which is cooled by the radiator return water, and then the fuel should leave there and go back the filter at not more than SEVENTY DEGREES Celsius, which is still hot enough to cook your dinner.
To help cool the fuel the TD5 fuel system circulates about a GALLON of diesel a MINUTE to the cylinder head and back again to the filter-head and fuel pump.
It is quite normal for the fuel filter to be too hot to hold onto after a decent run. Hot fuel burns cleanly in a diesel. So don't worry about it.
CharlesY