LONDON — Unemployment across the U.K. spiked sharply in August, a clear signal that the jobless rate is heading towards levels not seen in nearly 30 years when a British government salary-support scheme ends this month and new local restrictions are imposed to suppress a resurgence of the coronavirus.

The Office for National Statistics said Tuesday that unemployment rose by 138,000 in the three months to August from the previous three-month period. The unemployment rate jumped to 4.5%, its highest rate since early 2017, from 4.1% in the previous quarter.

So far, Britain has been spared the sharp rises in unemployment seen in the United States because of the government’s Coronavirus Job Retention Scheme, which has paid most of the salaries of workers who have not been fired. Some 1.2 million employers have taken advantage of the program to furlough 9.6 million people at a cost to the government of nearly 40 billion pounds ($52 billion).

Since the program ends at the end of October, many of those still on furlough are expected to be made redundant and unemployment to rise further.