The steering on my early Range Rover does not return to centre ( power steering )?

So if you mean the wheel is crooked while your going straight that's most likely a rack and pinion. But if you mean it just doesn't return to center after a turn then I would first check the fluid level. Usually with Low fluid there will be a grind sound as well when u turn. If that's not it then the alignment of your wheels can effect that as well. If it's not any of that then you must have a problem with either your front suspension (ball joints, tie rods ect.) or an issue in the rack and pinion or power steering pump in which case you may be better off seeing a professional technician. At least for a diagnosis

Yes, the first place to start looking is at your power steering. Early Range Rover means it is old. The mileage is probably high. I bet you haven't been diligent about changing the power steering fluid and perhaps the rack is the original. A steering rack handles high pressure and the seals are probably gone.

Take it to your mechanic, obviously the diagnosis and repair is beyond your skill set.

Yeah steering box to a selection of bloody big bars and ball joints,

any of which can wear/lock solid.

And I seem to recall many grease nipples,

which I doubt have ever seen a grease gun.

Of course it could even be a fault in one or more swivel hub ball joints

So your either taking it to a real mechanic,

Or you could start by removing say the pitman arm ball joint then seeing if you can turn the road wheel to left/right.

then working on to the next joint.

then the next.

Put it this way,

with the front up in the air and your hands at the 3 and nine position on a wheel if you push/pull it ought to move freely.

Has it had a suspension modification?

Even a 1 inch lift will alter the camber angles and stop.it self centering.

Get an alignment. No joy, rack is toast.

It may need a wheel alignment