Job vacancies in Britain slumped in April as uncertainty around the country's European Union membership referendum and the introduction of a higher minimum wage made employers more reluctant to hire, a jobs website said.

Job openings dropped by 9 percent in April from March and were down a hefty 27 percent versus a year ago, the survey by job site Indeed showed on Tuesday, a day before the release of official jobs market figures.

The monthly release said the slump in recruitment began in March and accelerated in April when the government introduced a new and compulsory higher minimum wage of 7.20 pounds an hour, up from 6.70 pounds for workers aged 25 or above.

"The combination of business uncertainty about the potential impact of a Brexit, the slowdown of the economy amid global economic headwinds and a sudden increase in the wage bill for many firms has triggered a sharp cooling in the jobs market," Mariano Mamertino, an economist at Indeed, said in a statement.

Britain's labour market has slowed in recent months along with the rest of the economy. The number of people out of work rose for the first time since mid-2015 in the three months to February, according to the most recent official data.

Most economists expect a British exit from the EU to hurt the economy, at least in the short-term.