Supermarket giant Tesco's defined benefit pension scheme deficit may have more than doubled since the company's last estimate in February 2016.
According to analysis by Exane BNP Paribas, the deficit may have increased by £3.3bn to £6.5bn.
Exane said the increase amounted to approximately 20 per cent of Tesco's £14bn market capitalisation.
But it said there was a "big caveat" in that estimating pension deficits was "a bit like estimating the content of two large black boxes".
"We have some help (asset allocation and sensitivity tables) but even when companies are calculating pension deficits, the only certainty is the estimate is wrong," the note said.
However Exane's estimate was close to Barclay's, which put the increase at £3.1bn.
Barclays based this on Tesco's own statement that its gross pension liabilities would rise by approximately £310m for every 10 basis point fall in the discount rate.
However, Barclays put the net deficit increase at £2bn.
Despite the ballooning deficit, Barclays predicted extra money would not be diverted into the scheme.
"Although [the increased deficit] is clearly unwelcome, we are very doubtful that this would lead to an increase in its annual £270m pension 'top-up'."
Tesco will release updated figures on 5 October, and could not comment on the estimates of Barclays and Exane.
In its last update in February this year, Tesco put its pension deficit at £2.6bn.
