Dr Hilary Jones added his own voice to the discord of Boris Johnson's own scientists over the Prime Minister's 'moonshot' Covid-19 testing plan.
Speaking at a press conference at Downing Street yesterday, Johnson said that mass testing would be piloted in Salford next month, and could eventually allow a return to a 'normal life.'
But minutes after he announced the plans, Chief Medical Officer Chris Whitty said the technology was not yet available, warning he should not put a date on when it would be because "that's not how science works".
The Prime Minister also said new types of testing, which are not yet available, will allow "millions" to be performed every day.
Addressing the plan on Good Morning Britain, Dr Hilary said: "We need to know that these tests are as reliable as the ones we're using in test and trace.
"We've got problems with that system already - it would be great if we had a rapid test later on within 20 minutes as to whether they were infectious or not.
"But the technology is not yet there - we need to know that it can be that reliable because it could be misleading and potentially harmful.
"And if we're going to do 10million tests a day, where are all these people going to come from carrying out these tests and processing them in the labs?
"It is such a huge ask and I don't think many experts believe it is achievable, even by next Spring. It's a massive undertaking."
Susanna Reid pointed out that Johnson said that one of the tests was a pregnancy-style test, which would mean they presumably wouldn't need a lab, just a saliva test.
"If it works," Dr Hilary suggested cautiously. "We haven't yet got the technology that proves yet that it works and even if we had these tests available at say sporting events where people are screened before they go into the event, the logistics of that are so immense and so mind-blowing.
"At an estimated cost of £100billion to do this a year, the same as we spend, almost, on the NHS in its entirety, which is £135billion.
"It is actually unachievable, I think."
*Good Morning Britain airs weekdays at 6am on ITV
