Mr Thorne stepped in as caretaker chairman of the group when the company's share price collapsed after a profits warning last year.
He replaced Roger Shute, the founder chairman who was the driving force as BM grew quickly in making aggressive acquisitions. Mr Shute retired through ill health at the same time as the profits warning.
Shares in BM peaked at 428p in October 1991. Yesterday the price rose from 19p to 21p. The Seaq system calculated the volume of shares traded at 1 million, unusually high for a company of BM's size.
It is understood that Mr Thorne is to take up a full-time executive position with another public company.
Moger Woolley, the chairman, has been attempting to draw a line under BM's troubled past by refocusing the group's operations and selling assets to reduce the debt burden.Reuse content