Update on this one.
I took the air hose off the throttle body and there appeared to be excessive EGR being returned even with the EGR solenoid unplugged.When some throttle is applied the gas flow is a massive.
I strongly suspect a blocked exhaust, possibly the catalyst. I'll get it next door onto the ramp later and have a look.
As it's a taxi and "We need the car" is the ruling they have applied I suspect it's been driven for ages with the engine light on and due to the split intake hose and jammed open EGR the exhaust is now all sooted up.
Shaun.