Staying in EU 'exposes UK to terror risk', says Iain Duncan Smith
Staying in the EU will make the UK more vulnerable to Paris-style terrorist attacks, Work and Pensions Secretary Iain Duncan Smith has told the BBC.
Mr Duncan Smith, who is campaigning for an EU exit, also questioned the effectiveness of curbs to migrants' benefits on immigration to the UK.
The senior minister's comments directly contradict David Cameron, who says the UK is "safer and stronger" in the EU.
He says the UK's future is in a "reformed" European Union.
The PM has also warned that leaving the EU would give the UK an "illusion of sovereignty" but not full control.
Mr Cameron's pitch on Sunday came as Tory London mayoral candidate Zac Goldsmith said he would campaign for exit - with Boris Johnson also expected to vote to leave.
Earlier, UKIP leader Nigel Farage had said a vote to leave would mean the UK was "in charge of our own country".
BBC assistant political editor Norman Smith said London mayor Mr Johnson had been genuinely conflicted but had now made up his mind - and was expected to announce he was joining the leave campaign.
Mr Cameron's latest comments came as ministers began campaigning to win over voters ahead of a referendum on 23 June over the UK's EU membership.
On the BBC's Andrew Marr Show, Mr Cameron defended his renegotiation of Britain's terms of EU membership, reached after two days of intense wrangling with EU leaders in Brussels this week.
He said he had secured reforms "people said weren't achievable", including curbs to migrants' benefits and exempting Britain from "ever closer union".
The offer on the table was a "better" deal for the UK and would be "legally binding", he said.
'Safety in numbers'
Making his case for why Britain should stay in a "reformed" EU, Mr Cameron said it would safeguard the UK position in the single market and help in the fight against terrorism and crime.
"Safety in numbers in a dangerous world," he said.
Proponents of Britain leaving the EU have argued it would give Britain back control of itself.
But Mr Cameron warned: "If we leave the EU that might give you a feeling of sovereignty - but is it real?
"Would you have power to help businesses not be discriminated against in Europe? No, you wouldn't. Would you have the power to insist European countries share with us their border information so we know what terrorists and criminals are doing in Europe? No, you wouldn't.
"So you have an illusion of sovereignty but you don't have power, don't have control, you can't get things done."
Mr Cameron also appealed to Mr Johnson not to join six ministers who attend cabinet in campaigning to leave the EU.
"I'd say to Boris as I say to everyone else - we will be safer, stronger, better off inside the EU.
"I think the prospect of linking arms with Nigel Farage and George Galloway and taking a leap into the dark is the wrong step for our country.
"And if Boris and others really care about getting things done in our world, the EU is one of the ways in which we get things done," he said.
BBC political editor Laura Kuenssberg says Downing Street has been resigned to Mr Johnson campaigning to leave following a meeting this week which left him disappointed with Mr Cameron's plans on the EU.
Also on the Marr Show, UKIP leader Nigel Farage criticised the scope of the PM's reform deal, saying it could be vetoed by the European Parliament and the European Court of Justice.
"There is one absolute certainty if we vote to leave... and that is that we will be in charge of our own country, we will make our own laws, we will run our own ministerial departments," he said.
He said the UK had ceded too much "control of our own future" to the institutions in Brussels.
A similar argument was put forward by employment minister Priti Patel, who is campaigning for an EU exit. She told the BBC's Pienaar's Politics that the referendum was a chance for the UK to "take back control".
By remaining a member of the EU, key decisions made in the UK risked "being ridden over roughshod" by the European Court and EU institutions, she argued.
On Marr, Scottish First Minister Nicola Sturgeon warned that if the UK voted to leave the EU but Scotland did not, it would "almost certainly" trigger demands for another referendum on Scottish independence.