Info on transit visa for airport transfer

[immihelp]

I am touring on Canada - Mexico- Costa rica - Panama- Venezuela and
Trinidad. I am travelling by British Airways ticket.
My returm from Port of Spain (Trinidad ) to Mumbai India is through
London. My flight to London arrives at Ghatwic AND HAS A CONNECTION TO MUMBAI FROM HETHROW AIRPORT.

I HAVE A VALID USA VISA BUT DO NOT HAVE A UK VISA.

KINDLY INFORM, IF I SHALL NEED A UK VISA AND IF REQUIRED, CAN I GET
IT FROM PANAMA? I AM AN INDIAN PASSPORT HOLDER.

[immihelp]

You need UK visa.

You need to get it from India before traveling.