Originally Posted by planes&trains

If you booked on ba.com, the BA allowance applies on UK (Vistara). I have done this multiple times.
On bags, yes. You need to collect them and clear customs in DEL.
UK will not accept your bags two days before a flight even if you take the bags to the counter soon after arrival.
If you remove items from the bag or repack, be prepared to be quizzed on why the weight on the original tag does not match the bag you are checking in.