only the Serjeant at Arms may enter the Commons chamber armed. With rising concern about the possibility that a vehicle full of explosives could be driven into the building, a series of concrete blocks were placed in the roadway in 2003. On the river, an exclusion zone extending from the bank exists, which no unauthorised vessels are allowed to enter. The Serious Organised Crime and Police Act 2005 formerly made it illegal to hold a protest near the Palace, or anywhere else within a designated area extending up to 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 These provisions were repealed by the Police Reform and Social Responsibility Act 2011, which replaced them with a total ban on tents and sleeping bags in Parliament Square, as well as a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. 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. Incidents The failed Gunpowder Plot of 1605 was a conspiracy among a group of Roman Catholic gentry to re-establish Catholicism in England by assassinating the Protestant King James I and replacing him with a Catholic monarch. To this end, they placed large quantities of gunpowder beneath the House of Lords, which one of the conspirators, Guy Fawkes, would detonate during the State Opening of Parliament on 5 November 1605. If successful, the explosion would have destroyed the Palace, killing the King, his family and most of the aristocracy. However, the plot was discovered and most of the conspirators were either arrested or killed while trying to evade capture. The survivors were tortured in the Tower of London, tried for high treason in Westminster Hall, convicted and gruesomely executed by hanging, drawing and quartering. Since then, the cellars of the Palace have been searched by the Yeomen of the Guard before every State Opening of Parliament, a traditional precaution against any similar attempts against the Sovereign. Sir Walter Raleigh was executed at the Palace of Westminster on 29 October 1618. The previous Palace of Westminster was