On 17 December, the FCA did make a public announcement, but only to kick back the timescale further. “The work is ongoing and good progress has been made, and all parties remain keen to complete this complex review quickly,” it said. “An announcement will be made as soon as possible in 2016.”

However, an announcement in April this year said only that, though a draft had now been prepared, there were “a number of important steps to be taken before the report is finalised”. Last week, the FCA released its latest update, announcing that the report was now complete, but that there remained “a number of steps for the FCA to complete before we are in a position to share our final findings”.

The repeated delays are likely to come under further scrutiny given the evidence in the RBS Files, which reveal that the bank’s strategy to make money when it drove businesses into its restructuring unit was laid out clearly in its policy documents, staff manuals, and financial records.

Tracey McDermott – who replaced Wheatley as head of the FCA – said under robust questioning from MPs on the Treasury select committee in April that she was not in a “position” to give a “definitive answer” about whether the report would indeed be published.

Tomlinson, the Department for Business adviser whose report on RBS triggered the FCA review, has raised concerns about Kingman’s backdoor contact with the regulator. “It appears that John Kingman, who worked for Treasury, was asking for information from the FCA about the report, which doesn't seem right to me,” Tomlinson told BuzzFeed News. “My recollection of John Kingman goes back probably about three years where he was very vociferously arguing for me not to publish my report.”

Tomlinson said he had been called to a meeting with Kingman ahead of publishing his report in which the official “was very angry about the report and indicated that it will be better if I didn't publish it”.

The independence of the FCA’s investigation into RBS has already been repeatedly called into question, after the regulator appointed the consultancy firm Promontory to conduct much of the work. Promontory paid $15 million to settle a dispute with the US regulators last year after it was found to have made changes to “soften” an internal review it had been hired to conduct into sanctions-busting and money laundering by Standard Chartered Bank.

The FCA quickly ran into difficulties after appointing Promontory, when the RBS GRG Business Action Group, which represents 379 firms that allege they were harmed or destroyed by the bank’s behaviour, said it was “not appropriate” that it had been asked to share evidence with a firm accused of “whitewashing”.

The FCA said in a statement: “Neither the email from the FCA to HMT on 3 July at 8.49am or on 30 November 2015 at 09.49 contains any price sensitive information or inside information. The contact with HMT concerned only the possible timing of any public announcement and was not relevant to our overall approach to GRG. At no time have HMT influenced, or sought to influence, the outcome of our work.”

The Treasury statement said: “The FCA has never shared any information regarding the content of the investigation with HMT, other than the expected timing of the conclusions. To be absolutely clear, HMT does not hold any information and has never sought any information regarding the ongoing investigation by the FCA, other than the expected timing, which is a matter of public record.

“Neither HMT nor any of its officials have ever expressed a view to the FCA regarding the outcome or content of the ongoing investigation. The ongoing investigation falls solely within the remit of FCA."

It said the departures of Wheatley and Kingman from their jobs were in no way related to the emails. “For completeness, the career decisions taken by John Kingman and Martin Wheatley are issues entirely for those individuals, and we would therefore state that these two issues are entirely separate. As set out in this letter, we refute any accusation of wrongdoing of any kind by individuals or HMT.”

In a statement following the publication of the RBS Files, the bank denied it had profited by destroying small businesses during the recession, but acknowledged, for the first time, that “a number of our customers did not receive the level of service they should have done” in GRG.

“We could have managed the transition to GRG better and we could have better explained to customers any changes to the prices or fees we were charging,” it said. “We also did not always handle customer complaints well. As a result, a number of our customers did not receive the level of service they should have done or, importantly, that they would receive now.”

But RBS still insisted “GRG’s role was to protect the bank’s position, where possible, by working with distressed businesses to return them to financial health”, and said it had seen “nothing to support the allegations that the bank artificially distressed otherwise viable SME businesses [small- and medium-sized enterprises] or deliberately caused them to fail”.