TORY high command began to hone its General Election campaign focus on voters’ fears that Ed Miliband could be “pushed around” by the SNP as far back as November 2014, Lynton Crosby, David Cameron’s election strategist, has revealed.

In a rare interview in his native Australia, Mr Crosby also noted how the Nationalists would “do well for a period,” stressing: “They are going to be around for quite a long time yet but the risk is expectations of delivery versus what they can actually deliver."

The Conservatives’ raising of fears during the General Election campaign about the prospect of a Labour-SNP alliance in a hung parliament was credited by many with securing Mr Cameron’s victory on May 7.

The Tories made great play of the possibility that Nicola Sturgeon and Alex Salmond with an enhanced SNP group at Westminster could be pulling the strings in a minority government led by Ed Miliband. Campaign posters to this effect appeared across many constituencies in England.

Mr Crosby, who also helped deliver two mayoral election wins for Boris Johnson and is known as the Wizard of Oz, said in an interview filmed by Sky News Australia: "Whilst it became fashionable towards the end of the campaign to report: 'Oh, there's been this surge in the SNP and that's upsetting the dynamic in Labour.

"The first time we picked that up was in November 2014 when in discussions, in focus groups, people said: 'Ed Miliband is a very weak man. If the SNP do really well and if he relies on them to govern, they will push him around. Who knows what we will get?'”

He added: "That was from the mouth of voters, well before anybody had picked up this sense. We started building on that then."

While Mr Crosby talked up the prospects of the SNP, he did not do so for Ukip.

"I don't think they've got a long-term future,” he declared, noting: "You should never write anyone off but they will be a voice of discontent.”

He went on: "They are very reliant on the performance of their leader Nigel Farage and even he couldn't win a seat. Sixth or seventh time he's tried to win a Westminster seat.

“He might be better coming to Australia and doing talkback radio than trying to run another seat in the UK," added Mr Crosby.