In an interview with the BBC, Balls said that Labour was committed to maintaining the value of the state pension but social security expenditure needed to be looked at “across the piece”.

He said that the party was likely to factor pensions into its calculations for a three-year cap from 2015-16.

Balls told Sunday Politics: “George Osborne is going to announce his cap in two weeks’ time. I don’t know whether he will exclude or include pensioners spending. At the moment our plan is to include it.”

He said the party would employ an “iron discipline” on spending if it returned to power and cap the amount spent on structural benefits as part of a new approach to welfare.

The Conservatives attacked the party’s plans through the Tory Treasury Twitter account, saying: “Basic state pension is excluded from govt AME cap but not from Labour’s apparently. Implication is clear – Labour would cut pensions”.

Labour dismissed the Tory line that it “would cut pensions” and said it supported the “triple lock” on pensions introduced by the coalition, which guarantees the state pension will rise by whichever is highest out of inflation, average earnings, or 2.5%.

But the party said it would be “peverse” to exclude spending on pensioners from the cap, according to the New Statesman.

Quoting a Labour source, the magazine wrote: “It would be perverse to exclude overall spending on pensioners and the impact of an ageing society from any sensible and long-term fiscal plan to monitor and control structural social security spending.

“That’s why we have supported increases in the retirement age as people live longer and why we have also said we would not pay the winter allowance to the richest 5 per cent of pensioners.”

Tory Treasury wrote: “Lab say would raise pension age to cut pensions bill. But govt plan is 66 in 2020 and 67 in 2026, and Lab welfare cap is 3 yrs to 2018 so either Lab wd accelerate rise to 66 before 2018 or they would have to cut pensions. Which is it @edballsmp ? What a shambles.”