By Paul Lewis
BBC Radio 4's Money Box
People in their 40s and 50s have been warned not to be "greedy" about their pensions.
Alan Pickering, former government pensions adviser and chair of educational charity Life Academy, said they must not take everything they are entitled to at the earliest age.
If they did the younger people in work who will create the wealth to pay for their pensions might refuse to do so.
Instead, he said those approaching retirement should work longer - even if it meant changing jobs - as a way of bridging what he called the "generation gap".
Speaking on BBC Radio 4's Money Box, Mr Pickering said: "There is still time to mend our ways and avoid the clash of the generations.
"But if people in their late 40s and early 50s, in both private and public sector pensions, insist on hanging on to everything they are expecting from the pension system, younger workers will resent it."
He said that people now paying in to a pension were not "buying and freezing loaves of bread". Instead the contributions were a down payment.
"We have staked a claim on the wealth that is going to be created by the next generation. But if we are greedy in that demand the next generation will refuse to pay for it," he said.
Mr Pickering said there was a simple solution - work longer.
"Extending working life is the key to bridging the generation gap. Not necessarily carrying on in your present job. But society must give you access to training so you can fulfil your potential once again in later life.
"We need a labour market that is blind to age."
Mr Pickering stressed he was not suggesting those already retired should give anything up - indeed they should have better state pensions.
"What we need is a state pension paid from a later age but a bigger pension to close the gap between the £84 a week of the present state pension and the £114 a week Parliament says we need to live on.
"We need to say to workers of all ages - and today's pensioners - we will have a much bigger state pension payable at a later age that will give you an absolute guarantee against poverty in old age and then have a system so individuals who save for themselves won't find that eroded by means-testing."
BBC Radio 4's Money Box was broadcast on Saturday, 25 November, at 1204 GMT and will be repeated on Sunday, 26 November, at 2102 GMT