Is it the fuel pump which makes the buzzing noise when you turn the ignition on? I can still hear it as normal, so if it is the pump I reckon it's working OK. I replaced the fuel filter about 2000 miles ago and it's been fine. No evidence of a leak. I'll try taking the hose off the fuel rail and see if any petrol comes out. As you said, it's unlikely all 4 injectors got blocked at the same time.
The air filter is due to be replaced but I reckon it's pretty unlikely it would stop the engine starting just like that. Surely it would struggle for a while first?
