A record 2.8 million people were out of work due to long-term sickness over the three months to February, ONS figures showed on Tuesday.
Numbers of 16 to 64-year-olds who were economically inactive also rose to a new high of 9.4 million - the highest level since 2012 in the wake of the global financial crisis.
According to the ONS, long-term sickness was the most common reason for people being economically inactive, meaning they were neither in work nor seeking work.
ONS figures also showed a monthly and annual rise in unemployment to 4.2% between December and March, fuelling hopes that the Bank of England would soon cut base rates.
However, figures showing a 6% growth in headline earnings, excluding bonuses, tempered the optimism.
“While tomorrow's inflation report will undoubtedly provide financial markets with a greater understanding of the timing around the first Bank of England rate cut, today's [...] highlighted the negative implications of keeping interest rates elevated for an extended period,” Scope Markets analyst Joshua Mahony said.
“Unfortunately, wages remain well above the levels that the BoE would have desired.”
Higher earnings growth than consumer price inflation, of 3.4%, “does at least ensure that the standard of living should be improving,” he added.