Contract attrition was cited for the drop in sales to £1.37bn (£1.51bn) in the half-year to June, though trading profits improved slightly to £37.6mln (£34mln). READ: Serco shares drop as it cuts revenue guidance amid 'less than ideal' market conditions Serco added it expects sales to remain flat for the next 18 months, though trading profit will grow this year to around £80m and rise again in 2019. Net debt at halfway was £220mln, and Serco expects a further rise by the end of the year.