UK Tier 2 ICT long term -extension query

Hi,

I have a query on my visa extension and found this link on the internet and thought that it is a good forum to post my question.
Below are my current visa details and entry and exit information and i would like to know for how many years i can extend my visa.

I am currently in UK and have travlled to UK with the same employer every time.
First entered uk in a business visa in Mar-2010 to May-2010
Enterted Uk again with Tier 2 ICT short term visa , entered Uk in July 2010 and left UK in May 2011(July-2010 to May-2011)
Got a visa for Tier 2 ICT short term from Aug-2011 to Sep 2012 - but didn't make a travel i.e. was not in uk from June 2011 to Aug -2012
Got a visa for Tier 2 ICTlong term for 3 years valid from Aug -2012 to Sep 2015 .
Entered Uk in Aug-2012 and currently in UK (in total have been out of the country for 9 weeks) and my visa is expiring in Sep 2015.

Could you please advise what options do i have for extending my visa and how many years at the maximum i can extend ?

Thanks in advance !!