The Institute for Fiscal Studies said young workers could get thousands of pounds less a year from the state if plans to introduce a single-tier state pension from 2016 are implemented.

The IFS said that someone who was born in 1986 and who spends 35 years as a low earner would receive nearly £1,000 per year less under the proposed new system than under the current system.

This figure could be nearly £2,300 per year for a high earner of the same age.

People close to state pension age would likely see no change in the state pension income, the think tank said.

The biggest gainers are expected to be those who have spent long periods out of work or doing low paid work – a group which disproportionately comprises women and the long term self-employed.

Under the new plans, which include replacing the current two-tier state pension with a single-tier pension set at £146 a week, women are set to be on average £5.23 per week better off, compared to £1.62 for men.

Those with more than 10 years in self-employment will gain £7.51 per week on average, compared to £2.19 among those who have never been self-employed.

Soumaya Keynes, a research economist at the IFS and one of the authors of the report said: “The single tier pension proposals will boost the state pension entitlements of some of those who are close to state pension age, particularly those who have spent time caring for children or who had long periods of self-employment.

“However, for most of those now in their twenties and thirties, although these reforms should make it easier for people to predict how much state pension income they will get, the reforms will also reduce the state pension income that they can expect to get. They will need to save more privately for their retirement to make up for this.”