It is nearly 20 years since the Bank of England was relieved of its responsibility for the “sponsorship of the City.” When the central bank was handed its independence from political control in 1997, the government took the view that the BOE should focus solely on maintaining monetary and financial stability, leaving others to cheerlead for the U.K.’s financial-services industry. Yet in recent weeks, the BOE has at times sounded again like an arm of the Treasury, if not a branch of the British Bankers' Association.

In a series...