I am traveling via London (heathrow) to India from USA. Should i apply DATV /TOWV ?

I am an indian national on a student visa F-1 in USA. I have booked my tickets by british airways ( to and fro) . Both ways i am stopping over in heathrow airport. I was aware of the transit visa requirement before booking, my agent here is SURE that i dont need one. I have looked at sources online, british consulate etc.. I see conflicting statements from people, and with what i understand from the consul's website is that i dont require one, under exemptions ( DATV/TOWV categories).. I am not going out of heathrow, will be at my gate to take my next flight, my stop over is for 3hrs only, i dont have to change the airport, my onward flight is the same day, i dont see a reason why i should still apply for one, since i dont have to go to immigration in heathrow. If any one has already traveled, or any thing you know authentically to share is appreciated ....thanks