The Civil Engineering Contractors Association (CECA) said ministers should "proceed with caution" in the wake of the vote to leave the European Union to stabilise the economy. However, the economic uncertainty could discourage investors that were previously being wooed for major projects, it fears.
CECA head of external affairs Marie-Claude Hemming said: "After a lengthy campaign, the U.K. public has voted to leave the European Union.
"The change in circumstance has unsettled the markets which, if unchecked, may discourage long term investment in UK infrastructure.
"The UK must act to secure its economy, but growth will only be delivered if supported by world-class infrastructure.
"CECA therefore calls on Ministers to now to first stabilise Government, then re-establish their commitment to the projects outlined in the National Infrastructure Plan, most notably HS2 and a third runway at Heathrow in order to maintain economic confidence following such a substantial change in the UK's relationship with the European Union and the rest of the world."