Layover at London or Paris with B2 tourist Visa

[izna009]

Hi Guys,

Can someone help me with this question. I am planning to take tickets for my parents in September & I can see some good deals in Qatar but they have stop overs either at London or Paris. I heard someone said that you cannot even stop for a layover at London Heathrow airport if you dont have a green card or citizenship with USA. Anyone with similar experience? Does anyone know how does that work.

Thanks
Izna