Downing Street has promised that Theresa May will stick to the Tory manifesto pledge of the triple lock, which guarantees rises in the state pension, after a former pensions minister said it would become unaffordable after 2020.
Ros Altmann, who left the government in July, called for the mechanism to be abolished and suggested that the prime minister could be more open to this idea than her predecessor, David Cameron.
A No 10 spokeswoman quickly dismissed the possibility of there being any risk to the triple lock before the next general election.
“The manifesto contains a commitment to protect the triple lock. That commitment still stands,” she said.
Lady Altmann had warned that the cost of keeping the safeguard would be “enormous” after the election in 2020.
The Conservative peer and pensions expert said she tried last year to persuade Cameron to drop the triple lock, 
under which pensions go up by the inflation rate, the growth in average earnings or 2.5%, whichever is the highest.
“The triple lock is a political construct, a totemic policy that is easy for politicians to trumpet, but from a pure policy perspective, keeping it for ever doesn’t make sense,” Altmann told The Observer.
“I was proposing a double lock, whereby either you increase state pensions in line with prices or with earnings. Absolutely we must protect pensioner incomes, but the 2.5% bit doesn’t make sense.
“If, for example, we went into a period of deflation where everything, both earnings and prices, was falling, then putting up pensions by 2.5% is a bit out of all proportion.
“Politically, nobody had the courage to stand up and say we have done what we needed to do.” 
Altmann also suggested that the triple lock could be abandoned now May is in charge, with the prime minister having shown herself to be willing to re-evaluate previously stated policies.
“With David Cameron, it was more difficult, it was his flagship policy. But from 2020, and even, you know, now, he is not there,” she said.
May’s joint chief of staff Nick Timothy said in an article for ConservativeHome last November that the obvious alternative to welfare credit cuts, looking at the triple lock, was “off the table” for the-then chancellor George Osborne.
“He could redistribute the welfare cuts to take the pressure off low paid, working people. But the obvious alternative is already off the table: pensioner benefits are protected and so is the ‘triple lock’, which means that the state pension goes up by the highest out of the growth of wages, inflation or 2.5%,” Timothy wrote.
Debbie Abrahams, the shadow work and pensions secretary, said it would be a “grand betrayal, a shocking broken promise hitting pensioners in the pocket” if the triple lock were broken.
“The lesson here is that for all their words about doing the right thing, the Tories don’t stand up for ordinary people,” she said.