My wife and I are US Citizens with passports traveling from Seattle to Dubai via London. We have a 9 hour layover in London Heathrow Terminal 5. We were planning to take a "layover tour" of London during this time. My travel agent is informing me that it is impossible to leave the terminal without claiming my luggage (big hassle) and that I will need a Dubai visa if I leave the airport but won't need a Dubai visa if I stay in the airport. Is this true? I find some of it hard to believe. Could someone please confirm this?