Inequalities in pensions benefits for widows and widowers from same-sex marriages created by the allowance of schemes to only backdate pensions to 2005 for civil partners, will be carried over from the civil partnership act, warn human rights groups.

Professional Pensions reports that the Marriage (same sex couples) Bill would not amend current inequalities which can occur in pension schemes for civil partners, which allow schemes to limit the survivors’ benefits to accrual from 2005, when civil partnerships were introduced in the UK.

When the issue was raised during the government’s consultation on the bill, the Home Office said: “To equalise treatment of all same-sex couples in a civil partnership or marriage with that of opposite-sex couples, would entail an unforeseen retrospective cost to schemes in a challenging economic climate when schemes are already under significant pressure.”

It added: “Many schemes (we estimate two-thirds) choose to pay exactly the same survivor benefits to spouses, civil partners, unmarried partners and unmarried same-sex couples on a voluntary basis.”

Rachel Robinson, policy officer for human rights group Liberty, said in response: “This bill is an historic moment for equality in Britain but Liberty is disappointed that it seeks to maintain a current inequality facing civil partners.”

Liberty represented John Walker, who in 2012 won a case to secure equal pension benefits for his civil partner. Ms Robinson warned that as the bill stands, more same-sex couples will have to go to court to fight for pension benefits equal to what a heterosexual couple would receive.

“If the bill remains in its current form same-sex married couples will have to seek redress in the courts,” she said.

“This represents on-going, direct discrimination and the courts have recognised as much.”

Appearing in front of the Public Bills Committee tasked with scrutinising the bill this week, Stonewall’s Ben Summerskill said he believed the issue would be addressed with future legislation.

He added that Stonewall had “persuaded” schemes to give equal benefits to same-sex civil partnerships as married couples in the past, and would continue to fight the inequality through establishing case law.