Any changes to the UK pension system must be affordable to the government, Work and Pensions Secretary John Hutton has said.
Meetings are taking place in six cities
His comments came as ministers held public meetings across the UK to debate radical reform of the pension system.
More than 1,000 people at events in six cities have been voting on ideas including raising the retirement age.
The government says it will look at the results before publishing its proposals in the next couple of months.
London, Newcastle, Birmingham, Glasgow, Swansea and Belfast hosted the consultations, which coincide with National Pensions Day.
Meanwhile pensioners' groups staged a rally in London to protest over the level of the basic state pension.
The government is working out what sort of new laws it should propose in its forthcoming White Paper on pensions, to be published later this spring.
Mr Hutton told BBC News 24 said people must recognise that any reforms had cost implications.
"I don't mean just affordable this year or next year but over the next fifty years because the one thing you've got to do in these arguments is to build a sustainable future.
"You can't ask people to plan and to save in confidence for their retirement unless they know exactly what they are going to get in terms of the state pension," he said.
Videos and votes
Lord Turner, who led the Pensions Commission, said he was confident the public would understand the need to work longer.
"As long as we explain to people what the reasons are for an increase in the state pension age, they will accept it," he told the BBC.
The audiences at the meetings have been selected by a market research firm called Opinion Leader Research, to provide the ministers with an audience that is a cross section of UK society.
Each audience heard speeches, watch a video presentation from Lord Turner and had the chance to ask questions.
Then they voted on different issues such as should the state retirement age be raised or should the state pension be more generous.
The Department for Work and Pensions said the information gleaned from the meetings would be analysed and taken into account while formulating the new laws.
Strong feelings have been stirred in the debate
The Pensions Commission report last November offered an extra £1.36 a week to the State Pension in 2010.
But Labour MP Kelvin Hopkins described the current situation as a "disgrace", and added that addressing it was"just a question of political will".
General Secretary of the National Pensioners' Convention, Joe Harris, said proposals had focused on future generations but something needed to be done for today's 11 million pensioners as well.
"Over 2.5 million older people are currently living below the poverty line, millions of women only receive a pension of around £50 a week and yet £2.3 billion in means-tested benefits goes unclaimed," he said.
"The government must recognise that means-testing pensioners has failed to get money to those who need it most, with 1.8 million people failing to get their entitlements."
The National Pensioners' Convention is calling for a raise in the basic state pension by £30 to at least £114 a week.