Do I need transit visa?

[Vsamsr10]

In 1 weeks times I have flight from USA to India. I have about 10 hrs layover in London. I was planning to go to the city for couple of hrs.
I am Indian. Have greencard. Do I need transit visa? Has anyone done this before?
PS: had posted earlier in wrong forum.

[ShaynaRussel]

I have been in the same situation as you. Stay calm. If you have a US green card and are an Indian citizen, you do not need a transit visa if you are just stopping over at the airport in London. However, when you leave the airport, it is different.

Geometry Dash Lite

[LCharge]

You can TWOV (Transit Without Visa) if you have a US green card and are just transiting through airport.