If so the unions, who help to choose the party's leader, could vote to install a favoured candidate, such as Alan Johnson or Ed Balls, both union-friendly cabinet members.

ECONOMIST: The trade unions are not as fearsome as they look

That means it is likely to be a busy year for Ed Johnson, director of science at the Staten Island Museum, which, with about 35, 000 specimens, said it boasts the largest cicada collection in North America.

WSJ: Bugged by Cicada Brood II? Don't Be

Mr Johnson and Labour leader Ed Miliband are among Labour MPs backing a change to AV - but many heavyweight figures within the party, including former Deputy Prime Minister John Prescott, and most Conservatives, are campaigning to keep the current first-past-the-post system for Westminster elections.

BBC: AV referendum: Union stance 'depressing', says Johnson