The swimming challenge was the brainchild of Trooper Clifford O'Farrell, whose legs were badly injured in an explosion in Afghanistan.
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City Hall has warned that Londoners should avoid coming to the centre of the capital on New Year's Eve unless you have a ticket.
Members of the Queen's Guard have been assigned the protection of armed police, amid reports they could be targeted by terrorists.
When Robin Ollington wrote to Buckingham Palace suggesting they introduce a Christmas tree, he didn't expect them to write back...