An increasing number of employers are finding it difficult to fill white-collar jobs such as those in finance or computing, a study shows.
The Recruitment and Employment Confederation (REC) said the availability of staff was falling, especially in London, which could face an "exodus" of businesses because of Brexit.
Candidates available for permanent jobs in the capital fell in March for the 46th month in a row, said REC.
Chief Executive Kevin Green said: "Finding people to do the jobs on offer is rapidly becoming employers' biggest headache and many are reporting an increasing number of white-collar jobs as hard to fill, including in the IT and financial sectors.
"Shortages of appropriately skilled, willing and able candidates was a problem before the referendum. Our concern is that Brexit will make the problem worse, particularly if onerous restrictions are imposed on people coming from the EU to work.
"Also, economic uncertainty about future prospects is having a detrimental effect on employees' willingness to risk a career move at this time, which seems to be driving down candidate availability. Our data shows London and the South, where financial services jobs are concentrated, as particularly suffering from low candidate availability for permanent job vacancies.
"This shrinking talent pool of available candidates means that businesses are boosting the starting salaries and hourly rates they are prepared to offer to the right candidate."