Intelligence chiefs fear terrorists could try to topple Big Ben onto the Houses of Parliament creating hundreds of casualties. A report by MI5 will today call for a raft of radical new security measures to protect Parliament - including a ring of steel around the Palace of Westminster. As part of the security measures, MI5 is reported to be planning to deploy agents to bases around the UK. The move is designed to combat the threat of home-grown Islamist terrorists linked to the al Qaeda network. Teams of intelligence officers, surveillance experts, analysts and computer specialists will be permanently...