Quinn will be responsible for Knowles' European and North American operations, and Charlton, who lives in Hong Kong, will handle the group's Asian, Australasian and Middle Eastern businesses. Roger Knowles will concentrate on growing the group and acquisitions.
Knowles said its profit for the six months to 31 January would be about £250,000, compared with £700,000 for the same period last year.
Profit has been hit by the economic slowdown but the group said it hoped for an improved performance in the second half of its financial year, once its overseas markets had recovered. It said that its full-year profit should be broadly in line with last year's pre-tax return of £1.65m.
Knowles warned last December that its first-half results would be lower than the previous year. The group said that its UK operations were performing well, whereas its overseas operations had been affected by the cost of entering new markets, including Italy.
Knowles was hit by a loss of £250,000 last April as a result of bad debts. These included an £80,000 loss caused by the collapse of contractor Christiani & Nielsen in 2000. The debt led to the firm taking out credit insurance in April 2001.