Markit's and the Chartered Institute of Purchasing & Supply's services purchasing managers' index (PMI) for the U.K. increased to 59.5 in April from 58.9 in March, beating expectations for a fall to 58.5. It was the highest level since August 2014.

The rise was driven by an increase in new business, stronger economic confidence and warm weather.

"Fears of the economy slumping amid election jitters are allayed as an upturn in service sector activity has helped offset sharp slowdowns in both manufacturing and construction," the Chief Economist at Markit Chris Williamson said.