The departure came as a surprise to staff at the merchant bank's head offices at Copthall Avenue in the City of London. Mr Seabrook had worked for FIM for 12 years, and he was responsible for managing around pounds 2.4bn in funds and a dozen staff. Prior to FIM, he had worked for Barings, the merchant bank.
Questioned about the reasons behind Mr Seabrook's departure, a spokesman for Fleming said: "He has resigned from Flemings by mutual agreement and he will now pursue his investment management career elsewhere. We wish him well."
The spokesman added that Mr Seabrook had left because he had helped FIM to achieve a certain level of success, and it was now necessary to push through certain procedural and structural changes to attain a new level.
Kenneth Ingles remains as chief executive of FIM, and is in charge of a total of pounds 24bn of funds under management.
Mr Seabrook's role will be split between John Rosier, who becomes head of UK equities at FIM, and several other unnamed business directors.
The spokesman said he did not know what Mr Seabrook would be doing next. As for any compensation for loss of office that may be paid to him or how much Mr Seabrook was paid while working for FIM, the spokesman declined to elaborate. "We never discuss that," he said.
Mr Garrett replaced John Manser as chief executive on 31 March when Mr Manser was appointed chairman of the Robert Fleming group. City sources suggested yesterday that other departures would soon follow, saying that they believed that Mr Garrett was keen to shake up staffing at the bank.