Former Prime Minister Sir John Major has warned a minority Labour government propped up by SNP votes would be a "recipe for mayhem".
In a speech in the Midlands today, Sir John said it would lead to a "weak and unstable" administration which would wreck Britain's economic recovery.
David Cameron has dismissed criticism about his tactics in relation to the SNP.
Speaking at a PM Direct event in Leeds he said: "All I am doing is pointing out what is as plain as the nose on your face - which is, right now, Labour is facing a wipe-out in Scotland."
SNP leader Nicola Sturgeon could present a potentially long-term problem for Labour.
Sir John will give a speech later today saying a Labour-SNP government would be "weak and unstable" and wreck Britain's economic recovery.