Why has the PM decided to take a tough line on immigration?

Lynton Crosby could be behind the tactic to focus on immigration

As a young MP in 2005, David Cameron was so disenchanted by Lynton Crosby's concentration on immigration during that year's general election campaign that he kept the issue out of his constituency pamphlets.

The Australian election guru had convinced the then Tory leader, Michael Howard, that his best chance of unseating Tony Blair was to appeal to "blue-collar concerns". Immigration was at the top of the list.

The tactic had been successful in Australia, but in the UK in 2005 it failed spectacularly. The "Are you thinking what we're thinking?" campaign, and messages including "It's not racist to impose limits on immigration", appalled critics inside and outside the Tory party.

Eight years later, and it seems the Prime Minister has had a radical rethink. Mr Crosby is back in charge of the Conservative election machine, and immigration is back in the news.

If Mr Cameron had any reservations over making immigration an election issue, he probably lost them following his party's humiliating defeat in the Eastleigh by-election. The party slumped to third behind Ukip. A poll found that 55 per cent of Ukip voters said they did so because they were worried about immigration.