The UK Serious Fraud Office [SFO] was set up in 1988 charged with investigating and prosecuting corruption and high-level corporate crime. For much of its life, it has been variously, incompetent, underfunded and neutered by political pressure.

In 2012, the SFO botched the investigation of Vincent and Robert Tchenguiz—London-based tycoons accused of fraud over the collapse of an Icelandic bank. The case had everything: dawn raids in ritzy Mayfair and Chelsea, billionaires in handcuffs and the possibility of recovering cash for victims. Everything, that is, except admissible evidence. The effort collapsed almost as soon as it reached a courtroom, when it turned out the SFO’s search warrants were unlawful. The judge called the agency’s work “sheer incompetence.”

Since the arrival of a new Director, David Green in 2012, it seems to have been turned into an effective law enforcement outfit. It’s scored wins against top-drawer companies such as Rolls-Royce Plc (for bribery) and convicted the ringleader of the effort to rig the Libor index and SFO investigators began inquiries into globe-spanning wrongdoing at Tesco and ICBC Standard Bank, which have led to $900 million in fines.

Last June the SFO charged Barclays, its ex-CEO John Varley, and three other former executives with fraud in connection with a deal that epitomized the global connectivity of London finance. In October 2008, Barclays was saved from collapse thanks to a $12 billion investment led by Qatar’s government. As part of the transaction, Barclays paid Qatar a secret $452 million fee for “advisory services” and loaned the country an additional $3 billion. To the SFO, the fee looked like a bribe and the loan an attempt by Barclays to illegally fund a purchase of its own shares. (The executives and the bank deny wrongdoing.)

For Teresa May, the success of the SFO is most unwelcome. Brexit talks are not going well and May is desperate to maintain the U.K.’s attractiveness to international capital after it finally leaves the European Union. The sudden emergence of an aggressive anti corruption agency is unhelpful to her pitch, which is aimed at such countries as China, Russia, and Saudi Arabia, not exactly models of financial probity.

Mrs. May is interested in eliminating the agency and to bring investigations under firmer government control by merging it with the National Crime Agency where white-collar cases would vie for limited resources with investigations into everything from cigarette smuggling to prison breaks.