When I transfer in Dubai (between the UK and Australia) I usually buy a litre of spirits and a few bottles of water. There have been various different procedures over the past 2-3 years.

I've always been allowed on board with water in sealed bottles purchased from the airport. That doesnt seem to be a problem in Dubai.

Regarding duty free, for a while you could buy your duty free but you couldn't carry it on board. It would be whisked away for pick up with your luggage at your final destination.

However, when I travelled back to the UK 2 weeks ago I was allowed to carry my dutyfree onto the plane as was usual pre 9/11.

I'm not sure what would happen if you purchased your duty free from the UK. The cashier SHOULD ask where your final destination is and then inform you of procedure. To be honest, with the exception of champagne and some of the fine wines, everything is cheaper in Dubai anyway.

I'm not to sure if travelling to Bangalore would be different.

Hope that helps!