Bank of England Governor Andrew Bailey said today he would look into how The Sun newspaper was able to report that the bank would expand its asset purchase programme by £150 billion, hours before it was officially announced.
Leaks of Bank of England policy decisions are almost unheard of.
But a series of government decisions on Covid measures, including economic support, have been reported in British newspapers ahead of their official announcement.
"Yes, we will look into it," Bailey told reporters when asked about the Sun report in a news conference after the BoE had officially announced the quantitative easing decision.
In its report first published online last night, The Sun said that unspecified sources had told it the Bank of England's stimulus would be larger than the £100 billion largely expected by economists and was "likely to be around £150 billion".
Before the announcement of the Bank of England decision at 7am, only the central bank and Britain's finance ministry would officially have known the decision.
A finance ministry representative sits in on deliberations of the Bank of England's Monetary Policy Committee, and Sunak must formally approve expanded asset purchases.
Michael Hewson, chief market analyst at brokers CMC Markets, said the apparent leak was "extremely concerning" and that there needed to be a full inquiry.
"These policy decisions are important macroeconomic events, and given the Bank of England also acts as a regulator, it's bang out of order," he said.
Last month Britain's Financial Conduct Authority concluded there had been no misconduct when a company contracted by the Bank of England to help provide video feeds of its public news conferences also sold traders slightly faster audio of the same event.
The Bank of England said its staff should have spotted what it viewed as misuse of its broadcast feeds sooner, and barred the business from working with it in future.
Meanwhile, the Bank of England today increased its already huge bond-buying stimulus by a bigger than expected £150 billion as it prepared for economic damage from new coronavirus lockdowns and the looming risk of Brexit.
The Bank of England raised the size of its asset-purchase programme to £895 billion, £50 billion more than expected by most economists in a Reuters poll.
The bank said that would give it enough firepower to stretch its buying of government bonds up to the end of 2021.
The Bank of England also cut its forecasts for the UK economy, which it now expects to exceed its size before the Covid-19 pandemic only in the first quarter of 2022.
Previously, it had expected the recovery be complete by the end of next year.
"The outlook for the economy remains unusually uncertain," the Bank of England said today.
"It depends on the evolution of the pandemic and measures taken to protect public health, as well as the nature of, and transition to, the new trading arrangements between the European Union and the United Kingdom," it added.
The Bank of England kept its benchmark Bank Rate at 0.1%, as expected in the poll, while it looks into the feasibility of taking borrowing costs below zero for the first time.
There was almost no mention of negative rates by the bank in the minutes of its meeting and its quarterly outlook report today.
It predicted Britain's economy would shrink by 2% during the fourth quarter of this year, as England re-enters lockdown, and fall by 11% in 2020, more severe than the 9.5% contraction it forecast in August.
Gross domestic product was likely to grow by 7.25% in 2021, weaker than a previous forecast of 9%.
Unemployment was set to peak 7.75% in the second quarter of next year, much higher than its most recent reading of 4.5%, the Bank of England said.
But its two-year inflation forecast remained unchanged at 2%, the central bank's target.
"Our view is that inflation will be closer to 1.5% by the end of 2022. That's why we believe the bank will still have to increase its policy support," Ruth Gregory, an economist at Capital Economics, said.
Britain's economy has been supported by a surge in debt-fuelled spending by the government and the Bank of England is buying up many of those bonds.
Despite the spending, Britain faces the worst peak-to-trough contraction of any Group of 20 economy, Moody's said on October 16 when it cut Britain's credit rating.
That was before Prime Minister Boris Johnson announced a month-long "stay-at-home" lockdown for England that came into force today.
Britain also faces the risk of a trade shock when its post-Brexit transition with the European Union expires on December 31.
So far, London and Brussels have failed to strike a new agreement.
The Bank of England's Monetary Policy Committee said trade would suffer even if there is a deal.
"There is uncertainty around the extent to which the initial adjustment to new trading arrangements with the EU will affect activity," it said.
"The MPC's projections are also conditioned on the assumption that cross-border trade falls temporarily in the first half of 2021 as businesses adjust to the new trading arrangements with the EU," it added.
GDP is likely to fall 1% in the first quarter of next year, limiting recovery from the fourth-quarter lockdown.