Trustees of nearly 400 insolvent pension schemes have been given six months to lodge claims with the Financial Assistance Scheme (FAS).
Pensioners have protested over lost pensions
This is the official rescue net for schemes which went bust between January 1997 and April 2005.
Members of pension schemes that have collapsed since then can claim instead on the Pension Protection Scheme.
The FAS will top up pensions to 80% of their expected level but only for workers close to retirement.
The rules mean that only those who would have reached their normal retirement age by 14th May 2007 will be able to claim, at least initially.
Terminally ill members can also claim regardless of age.
The promised pension will be capped at £12,000 a year.
However, the FAS excludes insolvent pension schemes where the employer continued to trade.
And critics say that only 17% of approximately 80,000 potential claimants will get any money over the next three years.
Ros Altman of the Pensions Action Group said: "I've got people in our group in their late 50s who've put all their life savings into their company pension scheme - because the government told them it was safe - who now face getting absolutely nothing."
The government argues that the scheme must concentrate first on those who are most in need - those closest to retirement.
And a spokeswoman for the Department for Work and Pensions denied that remaining scheme members would be left in limbo with no hope of rescue.
She said the government intends to review the funding and operation of the FAS in three years time, at which point a new tranche of claimants might become eligible for payouts.
Trustees of insolvent pension funds who wish to lodge a claim can contact the FAS Operational Unit on 0845 6019941.