Thanks - hot and cold running makes no difference, it struggles under load (3 adults) if I try and use third around 2000rpm (30 mph) going up even a gentle gradient, much the same for 4th at 40mph.
Other than that, it revs freely up to the red line, idle is smooth and hot and cold starting are both fine.
I'll have a look at the knock sensor tomorrow - does disconnecting it provide a decent test?