Two of the eight-strong Chesterton team have moved to other departments within the firm while the other six have joined competing consultancies.
Four have joined Donaldsons' London office, with the remaining two joining RPS and DTZ.
Guy Greaves, head of building and development services at Chesterton, said this week that the future of the firm's London planning office is under review. But he stressed that the company still has ten chartered planners at its other offices and that they provide services for clients throughout the UK.
The restructuring means that Chesterton now only has planning teams in its Edinburgh and Birmingham offices. Ian Anderson resigned as head of the London team this summer to join Donaldsons as a partner, taking the most senior Chesterton planners with him.
Anderson rejected suggestions that the planning team had been jettisoned because it was underperforming financially. He told Planning: "The reorganisation came about as a result of wider financial problems within the company."
CgMs director John Stockdale said: "In London and the South East, Chesterton will probably refer planning work to us under a consultancy agreement.
But to call it a strategic alliance may be putting it too strongly."