The prime minister has issued party members with a glossy instruction manual for campaigning in the election, which carries a warning that not getting supporters out to vote could cost the government 60 seats.

The PM, in the pamphlet "Choice for Britain", warns that apathy and cynicism, not the Tories, would be the government's biggest opponents.

If, as Millbank strategists fear, voter turnout hits an all-time low, the Labour majority could fall from 183 to 60.