David Cameron Speaks At The Conservative Party General Election Rally [Getty Images]

CORSHAM, ENGLAND - MARCH 30: British Prime Minister David Cameron speaks at a rally to mark the start of the general election campaign at Corsham School in Wiltshire on March 30, 2015 in Corsham, England. Campaigning in what is predicted to Britain's closest national election started today, after Queen Elizabeth II dissolved Parliament. (Photo by Leon Neal - WPA Pool/Getty Images)

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