The European Union needs the UK more than the UK needs it, according to the Vote Leave Campaign.
"We are the fifth largest economy in the world. We will be able to have a decent deal with the EU", said John Moynihan, speaking on BBC Radio 4's Today programme.
"The EU needs a trade deal with us more than we need a trade deal with them".
His comments follow yesterday's remarks by a leading pro-EU voice that leaving the market would be a "huge risk".
Speaking on the same programme, the chair of Britain Stronger in Europe, Lord Rose, said full access to Europe's single market was vital for UK businesses and jobs.
'Fear, uncertainty and doubt'
But today Mr Moynihan said: "The other side are trying to create FUD - fear, uncertainty and doubt - they're trying to say, oh, it's terribly dangerous, a leap into the unknown to leave. Nothing will happen. As Stuart Rose himself has said, the day we vote to leave the EU nothing at all will happen.
"At the end of it we will have a relationship with the EU, it's highly unlikely that it will be the sort of disastrous relationship that they claim".
Asked how a trading relationship of the UK outside the EU would look he said: "Everybody agrees there would be a free trade deal with the European Union, they cannot afford not to have a free trade deal with us. They export far more to us than we export to them.
"The French export huge amounts of food to us. The French farmers would riot if they thought we were going to enter into a trade war".
But Lord Rose told the BBC that campaigns to leave the EU had not explained how the benefits of the EU single market would be replaced.
"Those who want Britain to leave Europe cannot guarantee that Britain will retain full access to Europe's single market. They are putting the benefits at risk. Their proposed deal, whereby Britain would somehow retain access to the single market without obeying any of the rules, is a fantasy."
The prime minister, who wants the UK to stay within a reformed European Union, is pushing to renegotiate Britain's terms of membership ahead of an in/out referendum, which must be held by the end of 2017.
If agreement with other EU leaders is reached next month, a vote could potentially be held as early as June.
David Cameron's four main aims for renegotiation
- Economic governance: Securing an explicit recognition that the euro is not the only currency of the European Union, to ensure countries outside the eurozone are not disadvantaged. The UK wants safeguards that it will not have to contribute to eurozone bailouts
- Competitiveness: Setting a target for the reduction of the "burden" of excessive regulation and extending the single market
- Immigration: Restricting access to in-work and out-of-work benefits to EU migrants. Specifically, ministers want to stop those coming to the UK from claiming certain benefits until they have been resident for four years
- Sovereignty: Allowing Britain to opt out from further political integration. Giving greater powers to national parliaments to block EU legislation
Referendum timeline: What will happen when?