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Writing in the Telegraph on Friday, Howard says Cameron's efforts to renegotiate Britain's position in the EU have been "met with failure" - something he blames on EU leaders and not on the Prime Minister.
Here's what he said:
"It is not his fault that those efforts met with failure. It is the fault of those EU leaders so mesmerised by their outdated ambition to create a country called Europe that they cannot contemplate any loosening of the ties which bind member states."
What Howard thinks is important for Cameron because Howard was such an important part of his political career. They were very close when Howard led the Tories from 2003 to 2005 and even delayed his resignation to buy Cameron more time to build the support he needed to become leader.
Speaking to the BBC's Today Programme on Friday morning, Howard outlined the reasons that he believes Britain will be fine outside of the EU, saying that Britain is a great country."
"We won't have a Norwegian agreement with the EU, we'll have a British agreement with the EU. We need a bit of self-belief and national self-confidence. We're a great country with the fifth largest economy in the world. Everybody wants access to our market. We won't be supplicants. We will have a sensible agreement with the European Union which would give their countries access to our market and give us access to theirs."
However, Howard's backing of Brexit might not be completely straightforward. He also writes in his Telegraph column that voting to leave might "shake Europe's leaders out of their complacency" and force them to offer Britain a better deal to stay in. Cameron has said that if people vote to leave the EU on June 23, he will instantly invoke "article 50" - the mechanism for leaving the EU. Howard told the BBC this morning that this is the wrong approach.
"I would suggest a slightly different approach, I think if we vote to leave, I think the sensible thing to do would be to wait a short period, perhaps a month or so, to give our partners in the European Union the opportunity to reconsider their position... if after a month or so they don't, then article 50 would have to be triggered."
Cameron, who wants to stay in the EU and therefore doesn't want people to use the referendum vote as some kind of protest vote, has called the idea that the vote could be used to get more things from the EU "for the birds."