Ending the triple lock guarantee on state pension increases would put more than a third of over-55s off voting Conservative, a poll by Old Mutual Wealth has found.
The triple lock guarantees annual state pension increases at the highest of inflation, earnings growth, or 2.5 per cent.
The government had previously committed to keeping the measure in place until 2020, but had made no promises beyond that.
But with a snap election called for 8 June, this timetable is no longer relevant, and prime minister Theresa May's government has not yet stated whether it intends to keep the triple lock in place if re-elected.
Old Mutual Wealth's survey of 1,000 people over the age of 55 found that if the government did opt to scrap the triple lock, 34.2 per cent would be "less likely" to vote Conservative.
This age group traditionally has a high turn-out rate - around 78 per cent in the 2015 general election, compared to 43 per cent of 18 to 24 year olds, according to Ipsos Mori - meaning a decision to scrap the policy could damage the party's chances of re-election.
Opposition leader Jeremy Corbyn, meanwhile, has already committed to keeping the triple lock in place under a Labour government.
On Friday (21 May), Ms May avoided revealing her plans for the triple lock, prompting Mr Corbyn to accuse her of dodging the question.
But while the triple lock is popular with older voters, industry and expert opinion broadly opposes keeping the 2.5 per cent guarantee in place.
In his recent state pension age review, John Cridland went further, recommending the link to inflation also be scrapped, leaving only a link to earnings in place.
Other independent experts who support scrapping the triple lock include former pensions minister Ros Altmann and Pensions Institute director Professor David Blake.
Old Mutual Wealth pensions expert, Jon Greer said the triple lock had become a "crucial election battleground".
"The state pension is one of the biggest costs to the public purse and the Office for Budget Responsibility projects it will cost 6.2 per cent of GDP in 2036/7, up from 5.2 per cent today, even though the state pension age is due to increase to 68 by then.
"In his report Cridland noted if the same rise in spending was faced today, this would be equivalent to a rise in taxation of £725 per household per year. On top of this, overall age-related spending is predicted to rise to more than a quarter of GDP by the middle of this century," he said.
Mr Greer argued for a link to earnings, but with an above increase measure when earning fell below inflation.
"As society ages, with more people reaching retirement age leaning on a smaller proportion of the population that are of working age, costs will become a significant burden.
"Any party that refuses to address the political hot-potato of the state pension could be accused of kicking the can down the road," he said.
However, he said the "power of the grey vote" could mean politics "rules over reason".
james.fernyhough@ft.com
