Keith Clarke, the chief executive of Atkins, insisted that the Metronet debacle was behind it as the company posted a 46% rise in first half profit.

Pre-tax profit came in at £42.7m, ahead of City expectations of £38m, after turnover rose 11% to £633.8m. The company also announced a £100m share buyback.

Clarke said: “Our balance sheet is exceptionally strong and we don’t have an acquisition pot to spend so we’ve opted for a buyback. We are still interested in acquisitions and will make them if they grow the company but we’re not interested in volume; it is quality we’re after with acquisitions.”

Clarke said operating margins had risen from 4.8% to 6.3%. He added the Middle East now accounted for 8% of workload and said he expected that to rise.

“We have 2,200 workers in the Middle East now, not just in Dubai. The Middle East economy is diversifying and we are doing, everything from rail design to urban planning.”

Operating profit at the design and engineering division, which accounts for 29% of turnover, rose 35% to £15.7m on the back of growth in nuclear decommissioning and work with Southern Water and Scottish Water.

Profit at the rail division fell slightly but the group said its renegotiated work with Metronet was profitable.

Last year Atkins posted an exceptional loss of £121m after the Metronet disaster.