What Hope 2018 said is correct. However, I would still suggest you to check with the airlines for the same as sometimes they do need a transit visa even if you are not stepping out of the airport. My sister faced an issue over an Australian transit visa though she just had a connecting flight from Sydney to Auckland.t
Thanks a lot
Had one more question has anybody booked tickets via London... did they have to take some sort of transit visa even if not stepping out of terminal or flying within few hours