State-backed funds from Kuwait and Singapore were among 16 investors given large allocations of Royal Mail shares as part of the company's contentious £3.3bn privatisation.
Sky News can reveal that the Kuwait Investment Office and the Government Investment Corporation of Singapore (GIC) were among the funds labelled by the National Audit Office (NAO) as 'priority investors' in a report which criticised ministers' handling of the postal operator's sell-off.
Both sovereign wealth funds remain shareholders in Royal Mail nearly seven months after the flotation, and at least one of them is understood to have added to its shareholding since the initial public offering (IPO).
The fact that two overseas state-backed funds were seen to have been afforded a form of preferential treatment may fuel the controversy over the sale.
The group of 16 investors was chosen by the Government's advisers as part of an attempt to establish a long-term investor base for Royal Mail when it sold shares in the company last autumn.
However, the NAO said that three-quarters of those funds had subsequently sold part or all of their holdings in order to cash in on the instant surge in Royal Mail's share price.
The precise size of the allocations given to the Kuwaiti and Singaporean funds is unclear, and the Government has so far declined to identify the full list of 16 names, citing commercial confidentiality.
Their status as shareholders was revealed by Sky News last year, but their membership of that core group of 16 had not been previously disclosed.
Vince Cable, the Business Secretary, and Michael Fallon, the Minister who oversaw the Royal Mail privatisation, will face questions from the Business, Innovation and Skills Select Committee on Tuesday, when they are expected to be asked about the allocation of shares.
Insiders said the ministers may choose to dispute the accuracy of the term 'priority investors' if questioned on the subject by MPs.
Discussions were held with more than 60 institutions regarded as long-term investors during the 18 months preceding the privatisation, with 21 of those still interested at the time the IPO took place.
Sixteen of those funds then placed firm orders for stock, having exerted significant influence over the pricing of the shares.
Among the others included in this list are understood to have been BlackRock, the world's biggest asset manager, Lansdowne Partners, a top hedge fund which is understood not to have sold a single Royal Mail share since the IPO, and Standard Life Investments.
On Monday, the chief executive of the City watchdog said that the 38% rise in Royal Mail's share price on its first day of trading did not warrant an investigation.
A BIS spokeswoman said the majority of the 16 core investors were still shareholders in Royal Mail.
"There was no agreement – gentleman's or otherwise – on the holding of Royal Mail shares by priority investors.
"As is standard practice for any flotation, we did not seek to lock any investors in as they would have paid less for a stock they could not trade."