The contractor reported steady growth in the first half of 2012 with underlying profit up 16% at £10.7m on flat turnover of £478m.
Most of the improvement was delivered by the infrastructure division, which mopped up several highways and Crossrail jobs.
Costain said tendering activity remained busy at the division, which also managed to lift operating margins in the first half of the year to 3.9%.
As a result, group forward orders are ahead of last year at £2.4bn, with over 90% repeat orders, including new awards and extensions to existing contracts. Preferred bidder work was maintained at over £400m.
Around £600m of revenue has been secured for 2013, and more than £1.4bn secured for 2014 and beyond.
Chairman David Allvey said: “We now meet the integrated service requirements of major customers, whose repeat orders account for over 90% of the order book and who are continuing to invest in essential infrastructure projects.
“Despite the ongoing challenging economic conditions, we remain on course to deliver a result for the year in line with the board’s expectations.”
Costain six-month trading by division
Infrastructure division: profit £10.9m (2011: £5.7m); turnover £279m (2011: £219m)
Environment division: profit £1.6m (2011: £6.7m); turnover £127m (2011: £160m)
Energy & Process division: profit £2.4m (2011: £1.8m); turnover £70m (2011: £89m)