We will have a 9hour layover in London, how do you know if you can leave the airport to see Buckingham palace?

You are classed as "in transit" you have a ticket to leave, the authorities assume you will be getting on the plane along with your luggage which will not be going with you to see Buck House !! so you are allowed to go anywhere you want, as long as you are back in time for your flight..Heathrow and Gatwick are not exactly in Central London so make sure you have enough time to get back !!