Young people must register to vote in the EU referendum as a low turnout could lead to Brexit "by default", ex-Labour leader Neil Kinnock has warned.
Lord Kinnock said he hoped young voters would back the UK staying in the EU.
His message at a London rally came as he and five fellow former Labour leaders tried to persuade the party's supporters to vote to remain in Europe.
Meanwhile, Vote Leave campaigner Boris Johnson said around 300,000 jobs would be created if Britain leaves the EU.
At a rally in London's Olympic Park, Mr Johnson said: "After we liberate ourselves from the shackles of Brussels we will be able to create hundreds of thousands of new jobs right across the UK."
However, Labour's Chuka Umunna, campaigning for the UK to remain in the EU, said the job claim was "embarrassing", adding: "If you want see more jobs in the UK, you should vote to remain in Europe."
Prime Minister David Cameron has said there would be less money available, not more, if the UK shocked the economy by deciding to quit the EU.
About six million residents have yet to register to vote in the EU referendum on 23 June, more than a million of them are under the age of 25.
Lord Kinnock said the outcome of the referendum was "vital to the future of British people of all ages" but "the longest and strongest effects will be felt by you - the young generations".
"The risk is, if we get a low turnout, regardless of what people's background politics is, that by default Leave could win," he said.
"Don't leave your destiny to others. Don't dodge your duty to yourself. Make sure that you are registered to vote by next Tuesday, 7 June. Then use your vote. Vote to remain."
The former Labour leader and European Commissioner said young voters should ignore claims made by Brexit supporters, dismissing their promises as "pure fantasy" and "pants", adding that "none of the figures add up".
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On Friday, leading Brexit campaigners said leaving the EU could allow millions more to be spent on the NHS.
Justice Secretary Michael Gove has called on the government to pledge an extra £100m a week, saying it could come from the UK's EU budget.
However, Lord Kinnock said claims that money would be freed up for the NHS and cuts in VAT, while the same level of support was kept for agriculture, science and small businesses, were "bogus".
"The reason, above all, why those promises are empty is because of the people who are making them," he said. "Look at those who lead for Leave - Boris Johnson, Gove, Grayling, Duncan Smith, Fox and Farage.
"Have they ever in their political lives advocated policies that would give priority to spending on the community and its needs, have they ever given priority to public spending on services and investment, have they ever been the friends of working people defending their employment conditions, have they ever wanted to commit a priority to combating poverty and disadvantage?"
In a reference to former Prime Minister Margaret Thatcher's comments on the EU, he concluded: "If I may coin a phrase - no, no, no."
'Bonfire of rights'
Lord Kinnock, along with Tony Blair, Gordon Brown, Ed Miliband and ex-acting leaders Harriet Harman and Margaret Beckett, have issued a statement saying: "If Labour stays at home, Britain leaves."
They warned of a "bonfire of workers' rights" if the UK voted to leave and of a "double threat" to Labour-supporting communities of a recession and a "Tory government with an emboldened right wing".
They pointed to UK membership of the EU single market and said jobs would be lost if Britain withdrew, adding: "Only Labour can save Britain from Brexit."
Image copyrightGETTY IMAGES
Image captionFormer PMs Brown and Blair signed the pro-EU statement
Those Labour MPs backing an exit say workers' rights are the result of action by the UK, not the EU.
The former leaders' statement comes amid a drive from both sides to persuade people to register to vote ahead of the 7 June deadline.
There has been concern in the Remain camp that Labour is failing to energise its supporters.
Party leader Jeremy Corbyn - who has previously expressed Eurosceptic views - has been accused of being "half-hearted" in his backing for Labour's position to campaign to stay in the EU.
This week he said there was an "overwhelming case" to remain in, citing issues ranging from mobile phone charges to clean beaches and protecting bees - but also called for sweeping reforms.
'Pressures set to grow'
The Leave campaign's NHS funding claim came in a statement from Mr Gove, Conservative MP Boris Johnson and Labour's Gisela Stuart, who chairs the Leave campaign.
They said: "As our population grows, and as we all live for longer, so the pressures on the NHS are set to grow."
If the country votes to leave, they said: "The government should use some of the billions saved from leaving the EU to give at least a £100m per week cash transfusion to the NHS."
Leave campaigners said that money would be over and above the prime minister's election commitment to an £8bn real terms increase in spending.
Another Leave campaigner, former Defence Secretary Liam Fox said it was not xenophobic to believe that if you increase the population by three million every 10 years public services would be affected.
"It becomes very difficult for local authorities to plan how many school places are going to be required and it's very difficult for the NHS to know how many doctors and nurses will be required," he said.
But Mr Cameron said: "Nine out of 10 economists say there'll be a profound shock if we leave the EU. That means there will be less money - not more.
"It's also why so many doctors and nurses support remaining in the EU."