JP Morgan told the government earlier this year that it thought Royal Mail could have an equity value of around £7.75bn to £9.95bn, according to Sky News City editor Mark Kleinman.
The government floated the company at £3.3bn earlier this month, launching shares at 330p. Taking into account the company's approximately £800m of net debt, Royal Mail was floated with an enterprise value of £4.1bn.
JP Morgan's valuation will fuel debate over whether the government undervalued the company in the selloff, but it also gives clout to the argument that banks involved in the pricing process were over-optimistic.
A spokesperson for the Department for Business, Innovation & Skills (BIS) said that a total of 21 banks pitched in May to act on behalf of the government on the sale. Seven of those were successful.
At the time those banks gave a wide range of valuations with a median around £3.6bn - but the BIS spokesperson notes that "proposals came months before any threat of strike action by the unions, financial market uncertainty in the United States and other factors which the Government has already said were taken into consideration in setting a price for the company in September."
Sky sources have reported that Citi and Deutsche Bank pitched well above the £3.3bn mark at which shares were sold. According to Sky sources, Citi had recommended an upper valuation of £6.5bn, while Deutsche Bank said it could be worth between £5.6bn and £6.1bn.
JP Morgan declined to comment.