<P> The Gentleman Usher of the Black Rod oversees security for the House of Lords, and the Serjeant at Arms does the same for the House of Commons . These officers, however, have primarily ceremonial roles outside the actual chambers of their respective Houses . Security is the responsibility of the Parliamentary Security Director . Parliament has its own professional Security force . Tradition still dictates that only the Serjeant at Arms may enter the Commons chamber armed . </P> <P> With rising concern about the possibility that a vehicle full of explosives could be driven into the building, a series of concrete blocks was placed in the roadway in 2003 . On the river, an exclusion zone extending 70 metres (77 yd) from the bank exists, which no vessels are allowed to enter . </P> <P> The Serious Organised Crime and Police Act 2005 made it illegal to hold a protest near the Palace, or anywhere else within a designated area extending up to 1 kilometre (0.6 mi) from Parliament Square, without authorisation from the Metropolitan Police . The Act also restricted the operation of loudspeakers in the designated area . These provisions were repealed by the Police Reform and Social Responsibility Act 2011, which replaced them with a total ban on tents and sleeping bags in Parliament Square, as well as a prohibition on the use of loudspeakers in the Square without permission from the relevant local authority . </P> <P> Members of the public continue to have access to the Strangers' Gallery in the House of Commons . Visitors pass through metal detectors and their possessions are scanned . Police from the Palace of Westminster Division of the Metropolitan Police, supported by some armed police from the Diplomatic Protection Group, are always on duty in and around the Palace . </P>

When was the present houses of parliament built