Source: BBCNews
Staying in the EU can be the "patriotic course for Britain", former M&S boss Lord Rose said as he launched the campaign for the UK to remain a member.
Lord Rose, Britain Stronger in Europe chairman, said leaving was "not worth the risk" and said Britain was "surely bigger" than "walking away".
The EU referendum is due to be held before the end of 2017.
A rival, Eurosceptic, campaign launched on Friday with the message "vote leave, take control".
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One of its supporters, Conservative MP Steve Baker, told BBC Radio 5Live leaving the EU was "the safer choice" as it would allow the UK to "take back power".
And Mayor of London Boris Johnson, speaking in Japan, said the price of leaving the EU was "lower than it's ever been" and repeatedly refused to rule out spearheading the "Out" campaign.
The Britain Stronger in Europe board includes former chief of the general staff Sir Peter Wall, West Ham United vice-chairwoman Baroness Brady and television presenter June Sarpong.
Speaking at the event in London, Lord Rose dismissed the idea that there was a "patriotic" case for leaving the EU.
"To claim that the patriotic course for Britain is to retreat, withdraw and become inward-looking is to misunderstand who we are as a nation," he said.
"I will not allow anyone to tell me I'm any less British because I believe in the strongest possible Britain for business, for our security and our society."
'Duty and obligation'
BBC political correspondent Chris Mason said this theme was a tacit acknowledgement that the rival campaign had "seized the patriotic label".
Britain Stronger in Europe are keen to avoid parallels with the Scottish independence referendum, when the No campaign was branded "project fear" by opponents.
Speaking on BBC Radio 4's Today programme, Sir Mike Rake, BT chairman, said the "In" campaign was "not trying to scare people" but said businesses had a "duty, an obligation and a right" to set out the effect on investment of a UK exit.
Former Prime Ministers Sir John Major, Gordon Brown and Tony Blair are supporting the campaign, alongside Labour MP Chuka Umunna, Green Party MP Caroline Lucas and Conservative MP Damian Green.