Unforeseen and unpredictable events often lead to halt of political campaigning

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Leaders of political parties did not hesitate to suspend General Election campaigning in the wake of the atrocity in Manchester.

The timing of an election is the subject of intense and meticulous planning at the highest level of politics, but parties are always aware that they must be flexible enough to respond to circumstances.

No terror atrocity on the scale of the Manchester attack has ever before disrupted a British general election. But some earlier campaigns have been thrown off track by unforeseen and unpredictable events in the outside world bursting into the political bubble.

Most recently, the EU referendum campaign was suspended for three days after the murder of Labour MP Jo Cox on June 16 last year, just a week before polling day.

Then-prime minister David Cameron and Labour leader Jeremy Corbyn joined Commons Speaker John Bercow and shadow foreign secretary Hilary Benn in a visit to Mrs Cox's Batley and Spen constituency to condemn her killing as an "attack on democracy".

In 2001, Tony Blair had to postpone an entire election by a month because of an outbreak of foot-and-mouth disease.

Mr Blair had let it be known that he had pencilled in the election for May 3 to coincide with local council polls, but delayed the votes until June 7 because of the difficulty of campaigning while the animal disease was being contained.

Some candidates in the French presidential campaign earlier this year suspended campaigning in the wake of a shooting in Paris two days before the first-round vote, which left one police officer dead and injured another.

In the USA, Republican presidential candidate John McCain briefly suspended his 2008 campaign to work on the erupting financial crisis, but Democrat Barack Obama declined to join him.

Candidates in the 2004 race halted all activities in the days after Ronald Reagan's death.

In 1952, Democrat presidential candidate Adlai Stevenson broke off from campaigning to take charge of the response to a prison riot in the state of Illinois, where he was governor.