1. There are no power issues. UK is 240v. No transformer needed.
2. Be careful about the airline baggage allowance re weight and size.
3. Check the internet, especially for special offers, ex-demo, etc. It is not unusual for ex-demo kit to be sold with discounts of 30% or even 50%. Expect it to still have manufacturer's warranty as of the date of your purchase --- although it is debateable how much good that is once brought to India. Otherwise, check out Richer Sounds. They have quite a few branches.
You are going to London? There are not as many hifi shops as you might think, in fact most of the high-end dealers are elsewhere in UK. It is nothing like Singapore, for instance. Still, there is enough to enjoy the shopping.
I can't offer anything more specific, as I have not been there for four years.