The estimated cost of pensions tax relief for employees to the government is expected to hit £24bn in this tax year, according to government data.
Another £16.9bn of national insurance relief on employer contributions will increase the total relief on pensions contributions to a record £41bn, HM Revenue & Customs (HMRC) predicted.
The figures are up £1bn since last year, and £6bn from the 2013/14 financial year.
The increase is largely down to the growth in the number of people saving into pensions, with more than nine million people now having been auto-enrolled since the programme was launched in 2012.
Barnett Waddingham senior consultant Malcolm McLean said the costs will only grow higher as AE minimum contribution rates rise over the next couple of years.
"In a slightly perverse way, it is the success of AE that is creating what is almost certainly a cost and affordability problem for HMRC," he said. "These costs will increase further as minimum AE contributions increase over the next two financial years, and then again thereafter as plans to scrap the lower earnings limit and extend eligibility to 18-years-olds are brought in.
"I am pretty certain that pressures on public finances more widely will force the chancellor to look again at the cost of pension tax relief and we can expect the next full Budget in the autumn to announce more changes involving further reductions in the annual and lifetime allowances and/or even the abolition of higher rate relief, politically difficult these measures will inevitably be."
Royal London director of policy Sir Steve Webb said another £14bn was added through relief on personal pension schemes, and the non-taxation of investment returns, bringing the total bill up to around £55bn.
Hargreaves Lansdown senior pension analyst Nathan Long added tax relief could also be hit by unexpected economic downturns: "While there is not the political inclination to change tax relief at present, if Brexit events were to send the economy into a tailspin, desperate times could call for desperate measures."
He also pointed out to HMRC's underestimate of 2016/17 tax relief figures, noting the overall figure was £750m more than anticipated, at £40bn. He said this could be caused by higher contributions made via salary sacrifice and increased contributions to defined benefit (DB) schemes under recovery plans.
Ahead of November's Autumn Budget, there was speculation chancellor Philip Hammond would slash higher-rate tax relief after he reportedly ordered civil servants to consider the policy.
Meanwhile, it has been warned that last month's changes to Scottish income bands - with six now in operation, compared to four for the rest of the UK - will cause confusion over the application of tax relief, leading to some either over-paying or under-paying.
Defined benefit (DB) schemes that provide GMPs must revisit and, where necessary, top-up historic cash equivalent transfer values (CETVs) that have been calculated on an unequal basis, a landmark court judgment said last week.
Regulators must act now to impose some "proper regulation" to stop another defined benefit (DB) transfer advice disaster, saysTim Sargisson.
Opportunities for defined benefit (DB) schemes to pursue investment approaches that help repair the UK’s economy cannot stand in the way of improving member outcomes, Aegon says.
More members transferred out of defined benefit (DB) pension schemes in October after September's record lows while values were surprisingly stable, according to XPS Pensions Group's Transfer Watch.
Joanna Smith says trustees will need to accurately identify if covenant issues are short-term affordability concerns, or the start of more material deterioration.