Britain had imposed a lockdown on March 23 in a bid to halt the spread of the virus, and launched a so-called furlough jobs retention scheme under which the government backs up employee wages.
But many other workers have been laid off, with companies including British Airways preferring to axe thousands of staff despite the state helping to safeguard jobs.
The nationwide lockdown is just starting to be eased and the government has said it will continue to pay up to 80 percent of wages until October.
"While only covering the first weeks of restrictions, our figures show COVID-19 is having a major impact on the labour market," said Jonathan Athow, ONS deputy national statistician for economic statistics.
The number of job vacancies sank in the three months to April to 637,000 meanwhile, or 170,000 fewer than in the previous quarter.
The ONS also revealed that the number of paid employees in April fell by 1.6 percent compared with March.
"Through April... there were signs of falling employment as real-time tax data show the number of employees on companies' payrolls fell noticeably, and vacancies were sharply down too, with hospitality again falling steepest," added Athow.
The British unemployment rate stood at 3.9 percent in the three months to March. That compared with 3.8 percent a year earlier.
The government furlough scheme is supporting 7.5 million jobs by ensuring that employees receive 80 percent of their monthly pay up to £2,500 ($3,100, 2,800 euros). Analysts stressed that the labour market would deteriorate even more sharply in the coming months.