Just as a final note on this,
I changed the hose clips on the fuel filter.
Engine ran better but still a little bit juddery and not as quick to start as usual.
I had a closer look and found that the water drain tap on the bottom of the fuel filter was weeping fuel slightly despite being fully closed.
Presumably also letting in air when the injector pump starts sucking.
So I unscrewed the whole assembly from the bottom of the fuel filter.
Completely unscrewed the drain tap and replaced the O ring on it.
Reassembled and all seem well now