Steve Smith, James Curliss, Russell Gillespie and Jeremy Phillips are due to start at Capita next month.
The four, led by Smith, a former Northcroft main board director, will concentrate on developing work in the London commercial market.
Alan Dickson, managing director of Capita's cost management arm, said he was delighted to have signed up the quartet. He said: "We needed four fresh faces to put us on the developer map in the capital."
Dickson added that the London office had more potential for growth than Capita's bases in Glasgow, Edinburgh, Sheffield and Manchester.
He said: "Our business in London has got to expose itself to commercial and retail developments in a big way. Being a public company, we have to grow."
The four will head a 30-strong team. Capita's QS division has a turnover of about £12m.
We needed fresh faces to put us on the map in the capital
Alan Dickson, Capita
Northcroft has already replaced the four executives, three of whom were regional directors, with Andrew Derwick, John Gray, Ivan O'Toole and Paul Heal.
Its London office will be headed by main board director David Claxson.
UK and Europe director Mark van den Berg played down the departure of the four. He said: "It's a shame. We wish them well but it creates opportunities for other people to step up. We are a big firm. Life goes on."
Northcroft has also expanded its main board from four to 12 to reflect the firm's increasing regional presence. Van den Berg added: "We wanted to broaden out the board into the operational centres."
The new board will include van den Berg, chairman Igor Rukuts and finance director David Orton, as well as regional chiefs Roger Birchenhall (Cambridge), Chris Burchell (Oxford), Alan Garbutt (Leeds) and Nick Howkins (Bristol).