A quick update on this issue.....
Driving to the Stealers this morning, no matter what I tried I couldn't get the mongrel thing to throw a fault code. When I got there the guy said without a fault code it was going to be hard for him to pinpoint the problem despite me fully explaining what the symptoms where, what type of driving seemed to make it happen more frequently and supplying him the fault code that my ODB-II software on the phone had captured.
Cut a long story short, he removed, drained and cleaned the fuel tank (which he said had about an inch of green jelly in the bottom of it). He cleaned the strainer on the bottom of the fuel pickup tube in the tank (which he said was almost completely blocked with some black crap that took him a fair amount of time to clean).
Asked him to clean the SCV and he said they didn't do that, all they could offer was to provide me with a complete new pump ($$$$) or a repair kit to service the pump ($$$$). Since I had seen the SCV's available for $225 elsewhere last night I decided that may be a cheaper option I will pursue without the Stealer's assistance.
Got the vehicle back after parting with just over $500 at around 330pm and after filling the tank I took it along some of the roads that it was throwing the fault codes on recently and although it spluttered at one set of lights, it didn't throw any fault codes (touch wood).
I think I will still replace the SCV because if there was that amount of sludge in the tank its probably a bit gummy and after looking at the threads about cleaning it yourself I think the $225 will be money well spent.
As usual, thanks for all of your help guys, as always, its very much appreciated.
Ash