The government will attempt to address inequalities in the state pension between civil partners and married couples as it considers marriage equality.
Yesterday's consultation on creating full marriage equality for gay people threw into question the way in which the Department for Work and Pensions (DWP) calculates state survivor benefits for widows and widowers from civil partnerships.
The current system provides widows and widowers of heterosexual marriages with different levels of survivor benefits.
In this system, when a man dies, his widow may be eligible for a survivor's pension based on all of his National Insurance contributions (NICs) from 1978.
However, when a woman dies, her widower may be eligible for a state benefit based on her NICs from 1988 only.
In civil partnerships, all parties are treated actuarially as married men for state pension purposes, yesterday's Home Office consultation revealed.
Helen Baker, partner at law firm Sackers, said: "If a civil partner dies, the surviving partner is treated as a widower so their state entitlement is based on NICs paid by the deceased from 1988, whereas heterosexual widows get an entitlement based on the NICs of the deceased for many years before that, so civil partners get far less."
The consultation published yesterday said that if marriage equality is implemented, the DWP is considering if and how it should extend its practice of treating all gay couples as married men from civil partnership to marriage.
Baker said the difference is due to the inequality inherent in the state pension system.
"State pensions are by their nature different for different people," she said.
"There are two discriminations here; one against widowers and another against civil partners.
"The ultimate equality would be to treat everyone as though they were a widow because women get more and this would be the reform to cause the least upset, but it will be more expensive."
The government's attempts to rectify inequalities within the state pension system have been met with anger form certain groups.
Last year's Pensions Bill confirmed the state pension age (SPA) will rise to 66 by 2020.
This will equalise the SPA between men and women, but means women face a far sharper rise in the SPA than men, sparking an outcry from women close to retirement.
Consultation closes 28 January
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