PTP in the year to June 30 climbed to £7.4m from £5.2m as turnover rose to £136.4m from £103.9m.

The group's environmental companies benefited from an expansion in the environmental and sustainability sectors. Its civil engineering companies exceeded revenue and profit targets for the year and generated 46% of UK turnover.

Contracts with councils, Network Rail, London Underground infrastructure companies and British Airways provided a steady flow of work in highway design and planning, rail station improvements and projects at Heathrow and Gatwick Airports, the group said.

It added that demand for its services was increasing despite uncertainty over the global economy.