British Prime Minister Boris Johnson said on Wednesday a programme to test and trace those suspected of having been in contact with people who have tested positive for COVID-19 would be in place by June 1.

Johnson, who himself was hospitalised with COVID-19 earlier this year, has been criticised over his handling of the coronavirus outbreak, with a suggestion that schools reopen to some pupils from June 1 challenged by some who say they should not do so until the true spread of the virus is better known through testing.

Earlier this month, Johnson unveiled a roadmap to ease measures that have closed much of the economy for weeks, including a move - at the earliest by June 1 - to begin the opening of shops and to return some pupils to school.

Speaking in parliament, Johnson said the government would have recruited 25,000 trackers by the start of next month, capable of tracing 10,000 new cases a day, when the overall number of daily tests would have reached 200,000.

"We have growing confidence that we will have a test, track and test operation that will be world-beating and yes it will be in place by June 1," Johnson told parliament in exchanges with opposition Labour leader Keir Starmer.

The test and track programme is seen as a key measure to reopen the country, but has also been dogged by criticism after opposition lawmakers said an earlier promise of a national roll-out of a National Health Service (NHS)-developed COVID-19 smartphone app had slipped from the middle of this month.

A Department of Health and Social Care spokesman said the government was "working at pace to develop our test and trace service, which will significantly improve our ability to track the virus and stop the spread."