Workers should brace themselves for a less comfortable retirement if Britain leaves the EU, David Cameron said as the fight for the support of older voters intensified.
A new poll of 8,650 over-50s found the referendum campaign had so far had little impact - with only 2% more voters having made up their mind in the last month and those splitting evenly between Leave and Remain.
The Populus survey, commissioned by Saga, showed Brexit narrowly ahead by 45% to 41% across the UK, but at least half of voters in Scotland, Wales and Northern Ireland were in favour of staying in.
Quizzed by Saga magazine on the key issues, the Prime Minister said divorce with Brussels "would put pensions at risk".
"Everyone - even those who want to leave - accepts there would be an economic shock. We owe it to all the people who have worked hard and saved all their lives to find dignity in retirement," he said.
He said uncertainty over visa and residency permit issues for the 100,000 skilled EU workers in the UK care industry would have an "unpredictable effect on frontline services".
Vote Leave chief executive Matthew Elliot told the magazine: "By leaving the EU and increasing our trade with the rest of the world, we would become far less vulnerable to being dragged down by the eurozone crisis.
"The value of pensions and investments depends above all on the fundamentals of the British economy."
He said there was "no question of throwing out Europeans who are already living here".
The poll found Leave was ahead by 47% to 40% in England but Remain led by 56% to 31% in Scotland and 50% to 43% in Wales and Northern Ireland.
Those in their 50s backed maintaining membership by 44% to 41% but other age groups backed Brexit - by 45% to 43% for voters in their 60s, 49% to 40% in their 70s, and 47% to 40% in their 80s.
Polling was carried out online between May 16 and 23.
A survey of users of the Gransnet website found more than half saying they would vote to Leave.
The survey of 1,024 users of the site carried out between March 24 and May 5 found 52% planned to vote Leave, with 38% supporting Remain. Just 7% said they did not now how they will vote.
Mumsnet and Gransnet chief executive Justine Roberts said: "The complex issues behind the decision over whether to leave the EU are causing head-scratching for a lot of voters, but Gransnet users are pretty decisive whichever way they're voting.
"Those who say they will vote to leave seem sanguine about how the UK would fare outside the EU."