Sorry, I forgot to mention that its a 1998 STi Type R (V4).

Fuel pressure was 36psi according to the gauge. I've now removed the adjustable reg and it's back on a standard Subaru one (partly to rule out any issues).

It's going in for a new Fuel Pump next Thursday and i'll throw on a fuel filter aswell in the mean-time.

Thanks for your help guys, it's been pissin me off for ages and it's the only thing that's been ruining what is brilliant car.

JK