Hi Dougie, To sum up, I flushed the PS system out twice with LR PS Fluid and changed the resevoir also, it did not cure the problem of heavy steering, the filter removed was dirty and blocked.

Plan B, bought 2 bottles PS flush fluid off evil bay for about £10, flushed out the system and fitted another new resevoir, now works perfect! I have another spare resevoir which I intend to swop with the one installed just so I can see the condition of the filter, I have a dentist mirror which fits into the resevoir for me to see.

weld spatter,iron filings, what ever you want to call it ? in my PS system it is very very fine particles of debris,all in all cost me about £100, when i do swop the resevoirs over in a few months i will use a syringe to draw out the fluid in the resevoir and leave the system full, 5 minute doddle

You could try the above just once and use the PS flush, LR PS fluid and a new resevoir for say £40 ish.  2014 Audi A4 Avant - Dont like it !
08 FL2 HSE AUTO, LOVE IT.
1999 ASTRA VAN,HAD IT FROM NEW.
KAWASAKI KH 250 B4.

*****UPDATE*****

so the PS oil was changed twice then flushed and then changed again and there was no change to the symptoms.
The PS pump was then changed as the original oil was black and smelt burnt and had debris in it.
The system was then flushed again and the oil changed twice more till the oil was cherry red after the steering had been used.

It drives like a dream now! The original pump that had been on the car from new had given up the ghost (189k miles) so i can't complain too much.

Cost - labour 1 x afternoon replacing and flushing oil, 1 x morning fitting pump then flushing and replacing oil twice, plus the cost of the pump.... £530. Ouch but not as bad as a rack.

Its just soooo nice to crank the engine and pull away without any hassle!

Thanks all for your support, I hope my experience may help someone else in the mystery that is diagnosing power steering faults.

What PS fluid did you use as you say its red, I thought it was supposed to be CHF202 which is green. 
Hung like Einstein, smart as a horse.