The Liberal Democrats have pledged to tackle the "gross injustice" of lower state pensions being paid to women.

Current rules, which are based on national insurance contributions, penalise those women who leave employment to care for their children, said the party.

Pensions spokesman Steve Webb said that the gap between pensions paid to men and women was being reduced at a rate of just 40 pence a year.

He proposed switching from the current system to one based on residency, which would ensure that women are no longer "reliant on their husband's pension".

In a £2.7 billion policy move, the Lib Dems are also pledging to boost pensions for single pensioners aged over 75 by £25 a week, and by £33 a week for similarly aged couples.

Webb said that "for generations women have been the poor relations when it comes to pensions".

"The government treats pensioners like second class citizens and female pensioners like third class citizens," he added.

"On present trends it could be 100 years before the typical woman retires on the same pension as her male counterpart."

Council tax

At the Bournemouth conference on Wednesday, the party also pledged that older citizens would benefit from plans to replace council tax with a local income tax.

Sandra Gidley, the party's spokesman on older people, said the current local taxation system was having "a hugely damaging impact on older people".

"It is time this regressive Tory tax was abolished," she said.