Hey Guys - would really appreciate some clarity here.

I am planning to travel from Mumbai to New York JFK via London Heathrow on Virgin Atlantic - Code Share with Jet Airways. The 2nd leg of the flight (LHR-JFK) is from a different terminal.

So basically I would be changing from Terminal 4 to Terminal 3, so would I need a transit visa? I have a valid B1/B2 US visa. Jet Airways wouldn't tell me if I need one and I can't seem to get through to the Virgin Atlantic customer care here in Mumbai.