LONDON, ENGLAND - SEPTEMBER 01: Prime Minister David Cameron (2L) walks to Parliament with his Director of Communications Craig Oliver (2R) on September 1, 2014 in London, England. Mr Cameron is expected to announce new counter-terrorism measures in Parliament. (Photo by Peter Macdiarmid/Getty Images)

LONDON, ENGLAND - SEPTEMBER 01:  Prime Minister David Cameron (2L) walks to Parliament with his Director of Communications Craig Oliver (2R) on September 1, 2014 in London, England. Mr Cameron is expected to announce new counter-terrorism measures in Parliament.  (Photo by Peter Macdiarmid/Getty Images)