The government said the mobile phone users were tracked via cellphone tower data, rather than via any apps (Image: AFP via Getty Images)
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Covid passports for theatres and sports are still being looked at, despite Boris Johnson delaying the end of lockdown.
Digital Covid certificates on the NHS app proving someone has a negative test or a jab are being piloted by officials ahead of 'Freedom Day' on July 19.
Reports had suggested the domestic passports, not to be confused with those needed for international travel, were set to be scrapped.
The idea has been hit with heavy criticism, with unions and MPs saying the certificates may infringe on people's civil liberties and lead to discrimination.
But Cabinet Office minister Michael Gove did not rule out them being introduced.
"We are running some pilots," he told the Mirror.
Minister for the Cabinet Office and Chancellor of the Duchy of Lancaster Michael Gove
"We are working with the FA, with the ECB (English Cricket Board) and others at a theatre level in order to build on the capacity of the Covid app to provide people with reassurance that venues are safer than they otherwise would be.
"But there is this extra four-week period, this regrettable delay, during this delay these pilots will put us in a stronger position to judge what the utility of the app might be.
"Ultimately, we want to be in a position where people can use the app for international travel and where domestically we can open up completely.
"But these trials […] will help us understand what the risks and benefits are."
Covid passports look doomed days before review as MPs say plans must be axed
The certificates were used by sports fans at England's opening 2020 game at Wembley on Sunday.
Despite the pilots, however, it seems unlikely that the passports will survive a parliamentary vote, however, as Labour and Tory backbenchers have said they will fight the plans.
A highly-critical report by a cross-party Commons' committee has also said the passports will will “disproportionately discriminate” based on race, religion, age and socio-economic background.