I will be traveling from India to Canada via United Kingdom in British Airways flight. The stopover in London is for 6 hours. I will be staying in the airport only. Do I need a transit visa for United Kingdom?
Assuming you have a visa for Canada (which you should to be able to fly there), you are exempted from the direct airside transit visa requirement, as explained on the gov.uk website. The rules for transit to Canada are the same than for US-bound travelers so the answers to this earlier question apply.