The superannuation savings of at least 13 current MPs - including the Finance Minister - are insulated from the recession because they are in a generous "gilt-edged" scheme that was closed to new members in 1992.

While many workers' superannuation scheme investments have taken a battering from the downturn, those MPs who were in the House before that year and are in the old parliamentary super scheme have a cast-iron guarantee on their entitlements.

The scheme closed to newcomers in 1992, but those MPs already in it were able to stay in and their entitlements are not affected.

According to the Register of Pecuniary Interests, 13 current MPs are in the old scheme.

Any who leave Parliament at the next election will qualify for payments of at least $87,300 a year - two-thirds of a backbench MP's $131,000 salary. Those who have been in Parliament for longer than 20 years will get more.

They can also cash in their entitlement - getting a return of twice the amount they put in as contributions. The level of the taxpayer top-up towards the MPs' own contributions of 11 per cent of a backbench salary has been valued at 23 per cent.

An annuity is paid to former MPs in the scheme who are over 50. It increases by the rate of the consumers price index each year.

The 13 MPs on the scheme are Speaker Lockwood Smith, ministers Bill English, Tony Ryall, Murray McCully, Nick Smith, John Carter and Maurice Williamson, Labour MPs Lianne Dalziel, George Hawkins, Ross Robertson and Pete Hodgson, Progressives leader Jim Anderton and United Future leader Peter Dunne.

Two MPs - Annette King and Trevor Mallard - were in the scheme but left Parliament for a time and could not start contributing again after they returned.

Sir Roger Douglas was already receiving his annuity when he was re-elected to Parliament. The annuity has been halted while he remains a member of the House.

While newer MPs choose their own superannuation schemes and are more susceptible to the vagaries of the investment market, the top-ups from the taxpayer are still generous.

For every dollar they put in up to 8 per cent of a backbench MP's salary, the taxpayer puts in $2.50.

By comparison, the public service super scheme provides a 3 per cent top-up and KiwiSaver has a minimum employer contribution of 2 per cent.

Pre-1992: MPs put in 11 per cent of the salary of a backbench MP (now $131,000) regardless of their actual salary. Contribution drops to 8 per cent after 20 years. The annual allowance after retirement is calculated by a formula depending how long the MP was in Parliament. Those in Parliament for 20 years got an allowance worth two-thirds of an MP's annual salary on the day they began to receive the annuity. It is pegged to the Consumer Price Index so increases every year. The value of the taxpayer contribution under the scheme has been valued at 23 per cent of an MP's gross annual salary.

Post-1992: MPs put in up to 8 per cent of a backbencher's salary. Until 2003 the taxpayer put in $2 for every $1 from the MP. In October 2003, the taxpayer contribution rose to $2.50 for every $1. MPs choose their own super fund scheme and are susceptible to investment woes. The maximum value of the top-up is 20 per cent of the MP's salary.