The major political parties have suspended national election campaigning after the London Bridge terror attack, as Prime Minister Theresa May chaired a meeting of the Government's emergency Cobra committee.
After consultation between the parties, national activities were put on hold until Sunday evening at least, with the position set to be reviewed later in the day.
But Ukip broke with the other parties by refusing to suspend its General Election campaign, with leader Paul Nuttall warning that stalling the democratic process could lead to more attacks.
Meanwhile Cabinet minister David Davis played down suggestions that the June 8 poll could be delayed in response to the second terror attack of the campaign period, saying he did not believe it would be legally possible.
The Union flag was flying at half mast over Downing Street as ministers and security chiefs gathered for the Cobra meeting, at which they were expected to hear an expert assessment of whether the UK's terror threat level should be returned to "critical" - meaning further attacks could be imminent.
Also present at the meeting were Home Secretary Amber Rudd, Foreign Secretary Boris Johnson, Defence Secretary Sir Michael Fallon, Health Secretary Jeremy Hunt, Transport Secretary Chris Grayling, Communities Secretary Sajid Javid and London Mayor Sadiq Khan, along with representatives of police and security and intelligence agencies.
Sunday's halt in campaigning is the second time that the election has been disrupted by terror atrocities, following a three-day pause after the Manchester suicide bomb of May 22.
The Joint Terrorism Analysis Centre moved the terror threat up to critical following the Manchester Arena attack, triggering heightened security measures including the deployment of military personnel to support police under Operation Temperer.
The threat level was last weekend lowered to the second highest category of severe, meaning an attack was judged "highly likely".
Political parties were quick to announce that they were putting their national campaigns on hold following the attack.
Labour leader Jeremy Corbyn said: "The Labour Party will be suspending national campaigning until this evening, after consultations with other parties, as a mark of respect for those who have died and suffered injury."
Liberal Democrat leader Tim Farron said: "The election must go ahead as planned. It is right that we suspend our national campaigning for a short while out of respect for those affected by these tragic events, but local campaigning can and must continue.
"The remainder of this campaign must be a collective showing of defiance and pride in our democratic values."
However, Mr Nuttall said: "The only guarantee that will come from our choosing to stall the democratic process again will be more attacks - it is what these cowards want us to do.
"For those of us seeking to serve the people of this country, it is our duty to drive the dialogue on how best to confront and defeat this brand of terrorism.
"That is what Ukip will be doing today and beyond. Therefore, I refuse to suspend campaigning because this is precisely what the extremists would want us to do."
The London Bridge attack, which killed seven and injured at least 48, was met by an outpouring of messages from election candidates of sympathy for those affected and praise for the response of the emergency services.
Mrs May said: "Our thoughts are with those who are caught up in these dreadful events."
And Mr Corbyn said: "My thoughts are with the families and friends of those who have died and the many who have been injured.
"We will stand together to defend our common values of solidarity, humanity and justice, and will not allow terrorists to derail our democratic process."
Mr Davis said he thought the break in campaigning would be "relatively brief" and that he believed election day was "locked in" to the scheduled date of June 8.
Asked by BBC interviewer Andrew Marr if polling day could be delayed, the Brexit Secretary said: "I'm not sure it can be legally done. In order to do this, you'd have to have some change in the law and who's going to do that?
"Parliament no longer exists. I'm not a Member of Parliament for the duration, as are none of the other people who were MPs."
Mr Davis said it "may well be" that the attacks were intended to disrupt the election, adding: "In which case, all the more reason not to defer, not to deflect, to as far as possible within the bounds of propriety to not let this pull us off course."
Shadow foreign secretary Emily Thornberry said: "The response from London should be to be brave, be calm, carry on, but also do not let this derail our democracy.
"We go ahead with this election and we make sure people vote."
Their position was backed by a number of senior politicians.
Conservative former foreign minister Alistair Burt said: "We don't have a Parliament or MPs at present. If there's no General Election, when would we get one?
"Must carry on. Parliament must be the national forum to decide response."
Conservative Steve Baker said: "We are without a Parliament to scrutinise and legislate until there has been an election. The election must proceed on schedule."
The Democratic Unionist Party's Ian Paisley Jr called for security to be stepped up at polling stations.
"People must feel safe especially at election time," said Mr Paisley. "Every effort must be made to protect polling stations across the kingdom.
"These terror attacks are attacks on our freedom and on our democracy designed to make us feel fear. Answer back with 'business as usual'. Madness to concede any ground to terror. Stand strong, democracy prevails."
The attack came five days before the election, with opinion polls suggesting great uncertainty about the outcome of the contest.
One new opinion poll by Survation for the Mail on Sunday put Conservatives a single point ahead of Labour, on 40% to 39% for Mr Corbyn's party.
However, the findings contrast sharply with a ComRes poll for the Independent and Sunday Mirror which still shows the Conservatives with a 12-point advantage.
Opinium for The Observer also has the Tories ahead but with the gap narrowing to six points.
Amid messages of sympathy and solidarity from MPs, there were signs of the terror situation becoming part of the political debate.
Labour's John Mann renewed calls for internet companies to be made liable for the content which their sites host, after long-standing complaints that terrorists are able to use social media to communicate with one another.
Former Ukip leader Nigel Farage said: "We cannot suspend the campaign and normal life indefinitely. We want real action from our leaders, not more hand-wringing."
And ex-Labour MP Simon Danczuk, who is standing as an Independent in Rochdale, said: "Can't believe public will now vote Labour to put Corbyn in Downing Street when he opposes shoot-to-kill and is effectively terrorists' friend."
Sunday morning TV political programmes, which would normally provide a vital forum for parties to push their messages as polling day approaches, were disrupted by the outrage.
The BBC cancelled its pre-election edition of the influential Andrew Marr Show, which had been due to feature election interviews with Mr Farron, Brexit Secretary David Davis and shadow chancellor John McDonnell.
It also cancelled Sunday Politics, which was going to feature interviews with Lib Dem former deputy prime minister Nick Clegg, Conservative Treasury minister David Gauke and Labour's Chi Onwurah.
Greens confirmed that they too were suspending national campaigning until the evening, though activities will continue at a local level.
Co-leader Caroline Lucas said: "My heart goes out to all those affected and caught up in these horrific and despicable attacks, and my thoughts are with the victims and their families.
"Deep thanks to our emergency services who have responded again with enormous bravery, and to the many members of the public displaying courage and compassion in the midst of terrible scenes."