Query regarding switching from tier-2 to tier-1(general)

[asap]

I have a Tier-2 (intra-company transferee) visa stamped in my passport which has been sponsored by an Indian company. This visa was stamped in India in January, 2009. Till now I have never travelled on the Tier-2 visa. This visa is valid till February, 2011.

Recently I had applied for Tier-1 (General) visa in India. At the time of applying I had requested for the Tier-1 visa to be post-dated. My tier-1(general) application was successful and the tier-1(general) visa has been stamped with a starting date in first week of May, 2009.

However, my Indian employer now wants me to travel to the UK urgently, to work from the UK branch office, for a period of 6 months.

I have been informed by others that my Tier-2 visa will continue to remain valid until the Tier-1 (General) visa comes into effect.

Following are my queries:

1. Could someone confirm whether my Tier-2 visa will continue to remain valid until the Tier-1 (General) visa comes into effect and until then whether I can travel to the UK on the tier-2 visa to work for the same employer who has sponsored the tier-2 visa.

2. If I can travel to the UK on the existing Tier-2 visa, and at the time of the Tier-1 visa coming into effect, if I am still in the UK, what has to be done to change my status from Tier-2 to Tier-1(General)?

In order to remain in the UK on the Tier-1(general) visa, after it becomes valid, would I have to leave the UK and pass through immigration to re-enter the UK on the Tier-1 visa OR would it be possible to change the status from Tier-2 to Tier-1(general) while I am still in the UK without having to leave the UK.

I would appreciate if someone could clarify these queries at the earliest. Thank you.