Drove the car last night, no problems. Today, the power steering is almost non existent at low speed. More noticeable when parking.
Have not had a chance to try or test anything yet. Where is the best place to start with diagnosis?

do you get assistance back with more revs at low speed?

fluid in the tank, rob?

Is the aux belt intact?

Any dash warning lights?

When stationary, no assistance. If I increase revs whilst stationary the assistance is normal. I get a clattery sound on full lock 1 in 4 turns roughly.
Belt ok as temperature not increasing and climate is good. No warning lights. Not checked fluid yet.

Had a look at things this morning and the assistance is now normal!! However there is a noise that sounds like a hammer drill when I approach and reach full lock. This is when steering both left and right when stationary.
Fluid level is normal and belt is intact and good. Am I looking at pump or pulley or what?

Or could it be as simple as a new belt?

Ok. The aux belt tensioner is very noisey. Could this be the cause of the above pas symptoms? Could it be this that was making the noise on full lock? That noise has not been replicated today.
Any help on this and I would be grateful.

I wonder if the tensioner pulley was partialy seized....I would get it changed asap (its easy and very quick to do)

Marks DTM Calib wrote on 13. Jan 2010 at 15:54:

I wonder if the tensioner pulley was partialy seized....I would get it changed asap (its easy and very quick to do)

I did regrease it about 3 months ago but I presume it is now dead. I will change it and the belt and see if that fixes the pas issue.  :y

I managed to get an assistant to turn the wheel to full lock whilst I was under the bonnet today. The pump is making the hammer drill noise.
Is it the pump thats gone or could the belt be jumping on the pulley?
I don't want to change the pump unnecessarily. 

Had similar noise last year new second hand pump sorted it. HTH