Car failed the MOT test on some simple things, but, more importantly, the power steering control valve. I rebuilt it 300 miles ago and they passed the car at that time - a year ago.

With the engine running and the car parked in the drive, the amount of play in the whole system is such that about 1 to 1.5 inches of steering wheel movement deflects the tyres.
So I would say thats about right for a stationary car - obviously, driving along the road it would probably take less than an inch. The steering seems very accurate to me. Is there any way to check the specs - and what are they ??

I need to convince the testing station here in the UK that its all working correctly.
Thanks,
Hugo.

If you have no lash in your steering box and all of your tie rod ends/drag links are tight, then the only thing left to be loose is the steering control valve. And that appears to be the problem your U.K. inspectors are having trouble understanding.

Tell them there WILL be a small amount of play in ANY power steering control valve.