Yet another update but it’s not fixed yet. 
so I made the 90 mile journey to the steering reconditioner. 
The car was scanned and it appeared the pump was performing properly with voltages and motor speeds all as expected. The chap thought it may be the rack that had been fitted 3 months ago. I agreed to pay for some exploratory work and after a few tests involving removing the fluid return pipe to the pump and seeing if fluid was still returned on full lock. The fluid was still being returned so no pressure was being built up so the piston in the rack is the suspect. 
I got a quote for a replacement but I would have to return at a later date. 
so on my return 90 mile journey I decided to visit the unit that had fitted the recon rack 3 months ago. I described the findings and the boss agreed it sounded like the piston but this was very unusual for the Fabia/polo racks. 
long story short, I’m taking it there in the morning to have another recon rack fitted under warranty. Fingers crossed!

 

As I type this, the steering is fixed and it was neither the pump nor the steering angle sensor. 
In fact the problem stemmed from the reconditioned steering rack that would not hold the pressure from the pump, just letting the fluid circulate. 
Yesterday, the chap scanned every aspect of the steering pump or steering angle sensor and no fault was recorded and everything was performing and displaying on the scanner as normal. As mentioned yesterday, on full lock the fluid was just being returned to the pump indicating a seal had gone with reference to the piston. That was checked today and the same fault was displayed when the connections to the rack were undone. Another reconditioned rack was fitted and so no more fighting the steering wheel on the way home. 
The lesson here is don’t just believe everything an apparent VAG specialist tells you as if I had had the new genuine pump fitted as was recommended I would be nearly £1300 out of pocket and the fault would still be there. 
So if the steering goes faulty, get the system scanned to check the pump is working correctly. Everyone said a faulty pump would put a light on the dash so if the pump and the angle sensor is performing properly on the scanner it has to be the rack. I had no light on the dash at all. 
The company I had the rack from tried hard to sort a replacement rack out for me ASAP once they knew what they were dealing with so thank you to them for excellent service this morning. Ultimate Recon in Birmingham.