The government has not set a deadline for public pension schemes to provide equal pension benefits for same-sex partners if a scheme member dies.
Elizabeth Truss, chief secretary to HM Treasury, declined to give a timeframe for the reforms in reply to a question from Labour MP Ruth Cadbury.
Ms Truss said: "HM Treasury will work with departments responsible for public service schemes to ensure that scheme rules are changed [...] as soon as practicable."
But she revealed all departments were "in the process of identifying members who will receive a change in entitlement, undertaking public consultations where necessary and then bringing forward the necessary regulatory changes".
HM Treasury announced in April public pension funds would have to change their rules to comply with the ruling of the Walker v Innospec case.
In July 2017, the Supreme Court ruled same-sex couples that were married or in a civil-partnership should have the same pension benefits as heterosexual couples.
Despite the changes for same-sex survivor benefits, the government isn’t extending the same treatment to male survivors of opposite sex marriages.
It has said this is because equal survivor benefits for male and female scheme members were required only for service from May 1990 and public service pension schemes already complied with this.
According to the Government Actuary’s Department, there’s an estimated immediate £1bn cost - before taking into account regular ongoing pension payments - associated with backdating survivors’ pensions beyond this date for male survivors of opposite-sex marriages.