Millions of new coronavirus testing kits could be ready days, rather than weeks or months, according to Public Health England.
It would show whether an individual had antibodies for COVID-19 which, if they did, would mean they could return to work if they were not showing symptoms.
Professor Sharon Peacock, director of the National Infection Service at Public Health England, revealed on Wednesday that millions of such a test have been ordered and could be used "in the near future".
However, England's chief medical officer Professor Chris Whitty was much more cautious about the tests and would not commit to a timeline for when they would become available.
"I do not think, and I want to be clear, that this is something we'll be ordering on the internet next week," he said.
Prof Whitty said the tests would first need to be evaluated, and then the main priority for testing will be identifying how many people have had COVID-19 without showing symptoms, and which NHS workers are very likely to be immune.
The test will then be "spread out" to the general population, he said.
Evidence suggests people cannot catch coronavirus twice in quick succession, if they have already been infected and recovered, the government has said.
The tests, which look similar to pregnancy tests, could be ordered on Amazon or taken at high street branches such as Boots, Prof Peacock said.
A Boots spokesperson has said the company is "keen to work with the government to explore opportunities to support COVID-19 testing".
"However we do not have any type of COVID-19 tests in our stores," it added. "Customers should not make a trip to a Boots store or pharmacy for this purpose."
The World Health Organisation has urged countries to step up testing in the global fight against coronavirus.
Mr Johnson has vowed to increase daily testing "from 5,000 a day, to 10,000 to 25,000 and then 250,000".
Appearing before the House of Commons science and technology committee via video link, Prof Peacock said the new tests were "rapidly" being evaluated at a laboratory in Oxford with 3.5 million having already been ordered.
"Further millions are being ordered today," Prof Peacock told MPs.
"But we do need to ensure we understand how they operate, because these are brand new tests."
Prof Peacock revealed the evaluation of the tests would likely be done by the end of this week.
She added: "In the near future people will be able to order a test so they can test themselves or go to Boots or somewhere similar to have their finger-prick test done."
Asked if the availability of the test to the public would be a number of days rather than weeks or months, she replied: "Absolutely."
But speaking during the government's daily press briefing on Wednesday, Prof Whitty said the tests would only be rolled out if they were shown to be accurate.
He insisted that "bad tests are worse than no tests".
Prof Peacock told the committee there are "two different models", with one possible model being a test that is ordered via Amazon and performed at home before being sent back to see whether someone tests positive or negative for coronavirus.
Another "might require you to go somewhere like Boots because it requires a blood prick", she added.
Explaining further how the tests would work, she continued: "It looks like a pregnancy test. Except that you're putting a finger with a spot of blood on there.
"You prick your finger like a diabetic would, then get a drop of blood and put it on a filter paper and then run some liquid to make that blood run into the test zone."
Public Health England will be asking some people to have a second blood test, checked with a "gold standard" test, to make sure the kits are working properly, Prof Peacock said.
The tests "can see if you have antibodies, in which case you know you had the infection", she added.
"This is not just for key workers, it's for the general population. Over time it's expected the proportion of the population will be positive.
"And that will allow them to get back to work."
Prof Peacock said she couldn't comment on whether the tests would be charged for but predicted there "would be an absolutely minimal charge if there was a charge".