We have had a couple of floating-mass fuel hose blockages just like that reported here in the past couple of months, aldot. I think it begins with water in the fuel tank, which grows something like algae. The algae dies when the water is drained and the tank is filled with petrol, but it continues to drift around in the tank. Eventually, when the machine is run out of fuel, it finds its way through the outlet fitting into the hose, and then it causes problems - it doesn't float back into the tank, but stays in the hose.
IIRC, we had one that lodged in the fuel tap and another one that plugged up the in-line filter. Both were delayed-action problems: the machine would run normally for a time, then stop mysteriously, but would start and run again after the floating mass had floated back up the fuel line.
