ONLY DO 19 MILE JOURNEYS .....THAT SHOULD CURE YOUR PROBLEM !

Seriously though PHIL is right it does sound like cr@p/fillerneck rust in the fuel lines if it's a gti it should have a plastic strainer in the tank the trouble is that if you pull this out it can let more cr@p/rust through and in any case it can be a right bu66er cleaning the tank out .
However on thing to check , if it's a GTI, you may if you're lucky find a conical filter in the inlet side of the main fuel pump ( if it has 2 pumps) this can get clogged up .But it may already be too late for the injectors .
If its a carb version then its just a case of cleaning it out an blowing the lines through.
Obviously in both cases it will most likely need a new filler neck ..... There was a firm doing stainless steel ones maybe a good investment .

Anyone else like to add anything that I may have missed

?