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St Mary's Axe, knicknamed The Gherkin, home to Coutts, the private bank
That's according to reports from Global Capital and The Wall Street Journal.
Global Capital reports that regulators have contacted Bank of America Merrill Lynch, Credit Agricole, Credit Suisse, and Nomura in relation to a possible investigation into manipulation in the British government bond market.
They have not yet alleged any wrongdoing.
The Department of Justice launched an initial inquiry last year, according to Global Capital, but is working together with UK regulators as the traders are based there.
The Journal reports that Lloyd's bank is also being investigated by the UK's Financial Conduct Authority.
Reports of similar manipulation in the US surfaced last fall.
A federal antitrust lawsuit filed in August claimed that US Treasury dealers including Goldman Sachs, JPMorgan, and Morgan Stanley coordinated to manipulate primary market Treasury auctions.