Tier-2 overlap

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My Tier-2 visa is valid from 1/9/2009 to 30/9/2012. I was offered a new job and I intend to commence on 1/7/2012.

1) Would BA allow me to work from this date (1/7/2012) or I will be issued new Tier-2 visa only from 1/10/2012?

2) If the latter is the case and my current contract expires on 31/8/2012 does it mean that I will not be able to commence my new job (with a new employer) before 1/10/2012?

3) If BA takes into account my circumstance and issues me visa from 1/7/2012 would the visa be issued for 24 months only (till 31/6/2014) – and if yes, will I be eligible for permanent settlement although my visa would expire 2 months before I met 5 years threshold? (i.e. from 1/9/2009 to 31/6/2014)?

Many thanks