Conservative candidates have been instructed to put attacks on Ed Miliband at the heart of their campaigns in a briefing message from Tory Headquarters.

The message delivered to candidates, seen by Sky News, is to focus on the "chaos" of a Labour pact with the SNP in interviews and at hustings.

As the row over personal attacks on the Labour leader intensifies, the 88-page document suggest the Conservatives will focus on negative campaigning.

There are 99 references to Mr Miliband in the "Notes for Speakers" briefing and just 10 to Prime Minister David Cameron.

Conservative candidates are encouraged to tell the public that a vote for every other party is a vote for Mr Miliband.

The headlines of the document include: "Vote LibDem Get Miliband", "Vote UKIP Get Miliband", "Vote Green Get Miliband", "Vote Plaid Get Miliband", and "the SNP will prop up Ed Miliband".

It comes as the Defence Minister Michael Fallon was sharply criticised for making a personal attack on Mr Miliband.

Mr Fallon said Mr Miliband had "stabbed his own brother in the back" to become Labour leader and would be willing to "stab the United Kingdom in the back" to become Prime Minister.

Defending his comments on Sky News he said it was fair enough to point out that the Labour leader could not be trusted.

And he added he did not want Mr Miliband making a "grubby deal" with the SNP to put Labour in power that would see him trade in Britain’s nuclear deterrent - something the SNP want scrapped.

When challenged about the comments on the campaign trail, Mr Cameron said that the "personal is the national" when it comes to the person who becomes prime minister.

Other Conservative figures have questioned the "negative" tone of the campaign but privately Conservative strategists point out that a negative message was successful in Scotland.

Some Conservatives believe that the public need to be reminded that Mr Miliband could be heading to Number 10.

Mr Miliband said Mr Fallon had "demeaned himself and his office" by making the comments and said he was used to the insults.

Speaking in London he said: “The Conservative party can throw what they like at me, they can make all the personal attacks on me that they want to but I have got used to it and you know what, I'm resilient.

"And I'm resilient for one reason and one reason alone - because I am fighting for the British people in this campaign.

"I'm fighting for the kind of country the British people want, which I think is a country that is different from now and works for them in a way that it does not work for them at the moment."

Mr Miliband spoke of how the Labour leadership contest had left his relationship with his brother "strained" during the Sky News/Channel 4 Battle For Number 10 Programme.

UKIP economic spokesman Patrick O'Flynn said Mr Fallon’s "meaningless" personal attacks should stop and added: "We think it is a bit odd that Michael Fallon should be trying to link defence of the realm to the way in which Ed Miliband became Labour Party leader."

The Conservatives have issued a number of attack adverts on YouTube and published unflattering pictures of Mr Miliband on the campaign Twitter feed.

Labour strategists say Mr Miliband’s poll ratings are going up.