Well after a long weeks wait all the bits for the install are here, fingers crossed everything works ok. I have a late prefacelift car with the facelift style dash which makes the DD possible.
After much mooching about on line I decided to go for a Pioneer App Headunit, basically there's no CD slot and everything is linked straight from your iPhone (4/4s) as the update for the iPhone 5 isn't out yet these can be had for less than half of the original RRP and I have no intention of upgrading any time soon. When it comes to the facia, fitting kit and ISO connector you have to shop around as prices vary, I got mine from 3 different places and saved around £40.
The jury is out on this being an easy install, time will tell. I'll update once I get started.