Markit's and the Chartered Institute of Purchasing & Supply's construction purchasing managers' index (PMI) for the U.K. dropped to 52.0 in April from 54.2 in March, missing expectations for a decrease to 54.0. It was the lowest level since June 2013.
A reading above 50 indicates expansion in the construction sector.
The decline was mainly driven by a drop in new work.
"UK construction firms reported their worst month for almost three years in April, meaning that the first quarter slowdown is unlikely to prove temporary," Senior Economist at Markit, Tim Moore, said.
"Softer growth forecasts for the UK economy alongside uncertainty ahead of the EU referendum appear to have provided reasons for clients to delay major spending decisions until the fog has lifted," he added.