Hello again
After my anger[:@] I have decided to call prodrive to see what the score is with this ECU, I gave them the numbers from it SP and A18-000DIX and 1001056110/9525 and they confirmed that this is in fact an ECU from a 1999 uk Impreza Prodrive Performance Pack and not for an STi, very nice bloke I spoke to told me that back in 1999-00 they used STi ECU's for their performance pack cars althought they have been altered for a non STi car they still bear the STi sticker, he told me this was completely fine to fit on my car without problem but recommended that i maybe should change the airflow sensor. thats it!
So it seems that the chap I bought this from advertised it all wrong, so panic over I'm happy now[]
Thanks for all your help everyone, and if you come across an STi ECU with the part numbers 1001056110 these are all PPP part numbers from UK cars and ignore the STi sticker
Take care