Should I apply for ILR or extension on my Tier 1 General?

[sonny79]

I have done my MSc from Staffordshire University, and then applied for and got my IGS after my Masters degree. When the IGS visa was about to expire I applied for HSMP (18th Feb 2008 ). I received the approval letter soon after. Sent out the rest of the documents and my passport to be stamped.
However, after that my application was under procession for two whole years. Whenever I would call the UKBA the only response I got was that the application was under processing (was being handled by some other department). I was never told why it was taking so long for it to be processed.
Then quite suddenly I received my passport with the visa stamp on 9th Feb '10 (expiring on 9th Feb '13).
I was wondering whether I am eligible to apply for ILR or would I have to apply for an extension for Tier 1 General?
Also what all documents would i need in either case?
A quick reply would be greatly appreciated.

[Lucapooka]

Extend then apply for ILR in 2015. IGS can't be aggregated with HSMP/Tier 1 to make up the residence period for ILR.