EU referendum: Lord Rose says it is 'patriotic' to remain in the EU
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".
- Follow video and text coverage and reaction with Politics Live
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.
EU referendum: What you need to know
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.
Vote Leave comprises a cross-party group of MPs and peers from the Conservatives and Labour, and UKIP's only MP Douglas Carswell.
It is being run by Taxpayers' Alliance campaign group founder Matthew Elliot, who organised the successful 'No2AV' campaign in the referendum on Westminster's voting system, and Dominic Cummings, a former special adviser to Conservative cabinet minister Michael Gove.
It has the backing of three existing Eurosceptic groups: Conservatives for Britain; Labour Leave and Business for Britain, and is being funded by party donors.
Leave.EU was formerly called The Know and rebranded when an amended referendum question was proposed. Founded by UKIP donor Arron Banks, it has been described by UKIP leader Nigel Farage as an "umbrella group" of anti-EU campaigners.
It describes itself as "Britain's fastest-growing grassroots organisation" and claims to have gained 175,000 members since The Know was launched in August.
Lord Rose, who was announced on Friday as the chairman of the campaign to stay in the EU, cited CBI estimates that the benefits of trade, investment, jobs and lower prices meant membership to the EU was worth £3,000 per year on average to every UK household.
He said: "When you consider that our annual contribution is equivalent to £340 per household, our contribution to the EU is an investment on which British families get a 10-to-one return."
The Conservative peer says the EU has to change but that to leave it would be too risky. He added, in an interview with BBC political editor Laura Kuenssberg, that he wanted to put the positive case for EU membership because those in favour of leaving the EU had launched their campaigns.
In pre-released extracts Lord Rose had been due to call supporters of leaving the EU "quitters", but he did not use that word when he delivered his speech.
"They have no idea whether we would be able to access Europe's free trade area, or what the price of admission would be," he said.
"They cannot guarantee that jobs would be safe and prices wouldn't rise.
"They cannot explain how we could stop free movement and simultaneously keep our access to the world's largest duty free market."
UKIP leader Nigel Farage, who is backing another campaign called Leave.EU, said the launch of the "In" campaign was "lacklustre, tired, dull, out of date and making a series of fallacious arguments that are not likely, frankly, to impress anybody".
The Electoral Commission has yet to designate the official campaigns on either side of the EU debate.
The chosen groups will benefit from increased spending limits of £7m during the campaign period, campaign broadcasts, and a free mailout to households.
They all get access to public meeting rooms and to the electoral register, and are entitled to public grants of up to £600,000.
The Electoral Commission has recommended voters in the election are asked whether the UK should "remain in" or "leave" the EU, rather than being asked to answer a "yes or no" question.
The government has tabled an amendment to the bill.