Trouble was signalled a fortnight ago at the group's annual meeting when the chairman, Neil Benson, disclosed that the managing director, Mick Jones, was leaving "to pursue other interests" and that Peter Kane, who founded the parcel and express mail company in 1971, would return as an executive director from 1 September.
It now emerges that the finance director, Torquil Montague-Johnstone, is also quitting in the next six months, "due to differing approaches".
Guy Buswell, currently responsible for Southern area sales, is joining the board as sales director.
Michael Kane, who was chief executive between 1995 and 1997 and like his brother is currently a non-executive director, has resumed executive responsibilities.
There are also plans to appoint two new non-executive directors shortly to replace the Kane brothers in those roles.
Shares in the group, which slumped from a June peak of 957.5p to around 620p after selling by Mr Jones and Mr Montague-Johnstone and the annual meeting statement, plunged another 52.5p to 575p as the scale of the board shakeup became clear yesterday.
Peter Kane expressed his regret that Mr Jones had decided to leave the company, but emphasised that it was "a personality matter, not a business- related decision". He said that Mr Montague-Johnstone was seeking other opportunities.
Mr Kane was also at pains to stress the good track record of the business and its continued buoyancy, high operating margins and improving sales.
He highlighted the 17 per cent rise in first-quarter sales which was reported at the annual meeting and "solid organic growth", pointing to benefits from new areas of development.
He added: "While there will be a more significant bias than usual in favour of the second half of the year, the board is confident of the outcome for the year as a whole."
In June the group reported pre-tax profits of pounds 19.1m in the year to March 31, up from pounds 16.1m the year before, on turnover of pounds 97.6m.
Peter Kane, 52, and his brother still own a combined 63.5 per cent of the company.
They floated their shares in June 1993 at 120p and stepped down as chairman and chief executive in 1996 and 1997 respectively.
Analysts are expecting group profits to rise from pounds 19.5m to pounds 22.5m in the year to March 1999.