Ministers hope most of the 500,000 residents of Liverpool will be tested for Covid-19 every seven to 10 days, as a possible route to ending England’s new lockdown on time on 2 December.
But there are big questions over how many people will volunteer for a test – because of the puny financial help for people forced to self-isolate – and full details of the scheme are yet to be thrashed out.
Yet, in a typically bullish message to the Cabinet, Mr Johnson said: “In addition to the better drugs that we now have, and the prospect of vaccine, we now have a system of mass testing.
“Rapid turnaround testing that I believe can be a massive and possibly decisive use to us in this country in defeating the virus.”
But Adam Briggs, senior policy fellow at the Health Foundation, said: “We don’t yet have a mass testing system in place across the country, although the pilot in Liverpool could really help.”
And Gabriel Scally, professor of public health at the University of Bristol, said the comments were all-too reminiscent of similar boasts about the potential for antibody tests, the test and trace system and the Covid app.
“From the prime minister’s comments, you would think we are going to sprinkle these tests around like fairy dust and the virus will disappear,” he told The Independent.
Within minutes of the Cabinet meeting, the prime minister’s spokesman admitted there was no date for when – or even if – mass testing would be introduced in other parts of the country.
“We will look at the result of the pilot and, when we are able to set out more details of the tests, that’s what we’ll do,” he told journalists.
There are suspicions that the announcement was brought forward to give ministers a promising headline ahead of Wednesday’s vote to give the lockdown the go-ahead the following day.
Joe Anderson, the Liverpool mayor, said he expects 70-100,000 people a week will come forward for a test – much lower than Whitehall’s figure.
They will be given the rapid lateral-flow tests using nose-and-mouth swabs or saliva – producing results in 15 minutes – but will also need a more reliable test, to obtain a back-up result.
This is to eliminate the 1-in-1,000 risk of a false positive, which is significantly higher than the equipment used in testing carried out so far.
Yet Mr Johnson told his Cabinet: “The test can establish within minutes whether or not you’re infectious, they are easy to use yourself, they are reliable, they are cheap.”
Mr Briggs added: “If it is to have any meaningful impact on reducing the spread of Covid-19, then any testing system needs to be accompanied by a strong support offer for those needing to isolate, and an effective and timely contact tracing system to ensure that outbreaks are identified early and onward spread is limited.”
Christina Pagel, research professor at University College London, warned: “Testing someone doesn’t stop Covid on its own. The big barriers to isolation are financial and practical – people need to earn money and people need to leave the house for caring responsibility.”
And Justin Madders MP, Labour’s health spokesman, said: “We all want this latest initiative to succeed, but for the prime minister to claim the system is working before its even started is the latest in a long line of grand claims made by him during this pandemic – most of which have seen him overpromise and underdeliver.”
