Well, having read the 'Engine replace' thread, I did a bit more digging about the water pump situation on the 1.9 diesel.
I ended up reading a few threads on Alfa Romeo sites and learned that the 156 amongst other models which I know use the same engine as the Saab/Vectra and BLS, had apparently had issues with water pumps failing.
So I was out checking over my own motor this afternoon and noticed that the engine castings had 2007 stamped on them, so seeing as the car was built in May 2008, I'm assuming the engine was built 2007/2008. Evidently, new water pumps were made and superceded older types, in August of 2009. I'm therefore assuming that as my engine is the Fiat/GM unit, it will most likely have the older type of water pump which I now find a little worrying! So much so, that I've sourced a revised genuine Alfa/Fiat branded water pump (40 quid and readily available on ebay) which I intend buying and a genuine Saab timing belt kit (£100) and getting the job done, but not until my warranty has run out this coming November. I've now just got to find out from my newly found Saab independent, how much he'll charge me to do the job!