Providing a decent pension for all is proving very difficult
The new state pension system, called personal accounts, will have only a "relatively small" effect when launched in 2012, research suggests.
It will be aimed at people who cannot or do not join an employer's scheme.
The Institute for Fiscal Studies (IFS) estimates that nearly five million people were unable to join a company pension scheme in 2005.
But the IFS estimates they would have accrued contributions averaging just £900 that year, under the new system.
"This suggests that the increase in pension saving, and therefore overall saving, brought about by the reform is likely to be relatively small," the IFS said.
The forthcoming system of personal accounts is aimed at people with earnings between £5,035 and £33,540 and who are aged between 22 and the state pension age.
The IFS looked at official survey data from 2005.
This suggest that there will be a large number of accounts with relatively small default contributions
It found that there were 4.7m people, 15% of the working population aged over 22, who had not been offered the chance to join a pension scheme run by an employer.
Of those, 3.7 million, or four-fifths, had made no alternative provision, such as a private pension.
The IFS also found that people who did not make pension contributions of any sort tended to be lower paid than those who did.
They had average earnings of £14,000 per year, compared to £21,600 for those who were already making pension contributions.
That meant that if the government's target group started to accrue pension contributions at the suggested rate of 8% a year (4% from their own pay, 3% from their employer and 1% from tax relief) then their average contribution would have been £900 in 2005.
In and out
Looking at other data for the five years from 2001 to 2005, the IFS found that there were 8.6 million people who had, in at least one of those years, not been able to join an employer's scheme.
It calculated that their average accumulated personal account, before any investment return, would have been just £2,820 during those years.
"Contributions were typically lower among those most likely to be moving into and out of the personal account default group than among those who remained in the group throughout," the report said.
"This suggests that there will be a large number of accounts with relatively small default contributions," it added.
The IFS estimates are different from those of the Department for Work & Pensions (DWP), which in 2007 suggested that between four and seven million people might join the personal accounts scheme.
In February, research by the department suggested that almost everyone who joined the scheme would be better off, even if they then lost entitlement to some state benefits.
The ground work for the new top-up pension system was laid down by the 2007 and 2008 Pensions Acts, which followed on from the recommendations of Lord Turner's Pensions Commission.
It was part of a series of reforms designed to improve the UK's pension system over the next 40 years.
To encourage greater pension saving, Lord Turner recommended that people on low and middle incomes should be automatically enrolled into their employer's pension scheme if they had not joined.
Alternatively, they should be recruited automatically into the new state-run pension fund if their employer was not providing them with a decent scheme to join instead.
The contributions will be invested and the money used on retirement to buy an annual pension, to add to income from the basic state pension, the existing second state pension, and any state benefits.
With poor investment returns and increased longevity driving up the cost of funding company pension schemes, some employers have recently announced plans to close schemes to their existing members.
Examples have been at Barclays bank, Morrison's supermarket and, potentially, the Royal Mail.
The employers' organisation the CBI, which has been critical of the cost of public sector pension schemes, said their cost was deterring private companies from bidding when services are privatised.
It said some firms interested in bidding were being put off by the prospect of having to pay between 25% and 50% of salaries for former public service staff they took on.
"The government policy whereby transferred staff retain their defined benefit pensions, and the optimistic funding assumptions behind this, have unfortunately created unfair competition between public and private sector providers," said a CBI spokesman.
"Some companies have now stopped bidding for contracts involving staff transfers," he pointed out.
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