Execution Noble, the City brokerage firm led by executive chairman Nick Finegold, has parted company with its chief executive, while a majority investment in the firm from Banco Espirito Santo (BES), a Portuguese bank, could also be in jeopardy.
Simon Brookhouse, the former head of equities at HSBC, has quit the firm after 18 months, leaving Finegold, the former head of equity sales at Deutsche Bank, as chief executive.
The reason for Mr Brookhouse's abrupt exit is not known.
An investigation by the Financial Services Authority into BES, centred on the bank's American activities, could further delay or possibly scupper the bank's attempts to buy a 50.1 per cent stake in the British broker.
BES was fined by US regulators earlier this year, prompting scrutiny by the FSA, which has to grant its approval before any deal can go ahead.
Mr Finegold, however, said he was confident BES's investment would not be stalled: "Things are proceeding as normal."