It says a lot that whereas the US President resides in a massive mansion and the Russian premier has a medieval fortress, our own Prime Minister has to make do with running the country from a modest terraced house. In this one-off documentary, affable English Heritage chief Simon Thurley looks at buildings as manifestations of power and charts the history and symbolism of Downing Street, the Kremlin and the White House and what they tell us about their respective nations. It's full of diverting details, including one neat architectural gag: when he redesigned the state rooms at Downing Street in the 1980s, architect Quinlan Terry included above a doorway, as a cheeky reference to Mrs T, a tiny goldleaf figure of a thatcher. Simon Thurley, head of English Heritage, takes you inside the buildings whose tenants rule the world.Love, hate, treachery, barbarity, and base politics have all left their mark, as the presidents and prime ministers come and go. But the buildings remain silent witness to their deeds, and misdeeds. Each of them is expressive of national character: the pokiness of Number 10, a reminder to prime ministers that they are our servants; the pristine set of the White House, a stage from which the planet is run; and the overpowering brutality of the Kremlin, testament to so many dark deeds, and the line of unchallenged power that links the Czars to Russia's present day leader. The programme enjoys unique access to these places: the Russians even cleared Red Square for Simon, so impressed were they by the Queen's adviser on architecture. And it poses a key question. In the age of international terror, as these buildings defences are shorn up, are their inhabitants increaingly divorced from the very people they're supposed to serve, by the places they work in? The decision to go to war, the decision to assassinate, is now so much more easily taken from within their walls. So are we, just as much as they, prisoners of the Powerhouses?