Upvote:3
If you can check-in and pass security more than 2 hours before the flight is due, you could pass through at terminal 4, and use the inter-terminal buses on airside. I have not used those buses so I am not really sure that you will not have to show that you need to be at the other terminal. But I do know that the buses do run between the terminals, airside.
Added after further reading:
Looking at one of the other questions on this site I would say my suggestion is not going to work: Can we switch terminals at Heathrow (LHR) for shopping only? states that you need a boarding pass for a flight leaving from the terminal before you are allowed on the inter-terminal bus.
Upvote:6
You have two options: contact World Duty Free, as @JoErNanO indicated in his comment, or contact Heathrow Airport directly.
Heathrow Airport has a section dealing with media and filming: http://mediacentre.heathrow.com/filming_permits - while main focus is on news filming, from that page you can deduce that they entertain non-news filming and photography as well. From that page:
For non-news filming or photography, please contact [email protected]