A "good" antibody test could be available in a month, the Government's testing tsar has said.
Professor John Newton said those involved in developing such a test believe it could be ready by the end of May or early June.
Earlier this week Health Secretary Matt Hancock said that so far there is no antibody test that is "clinically valid".
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An antibody test that could be used to show substantial numbers of people had previously had the virus and gained some level of immunity is widely thought to be a key route out of the lockdown.
But the World Health Organisation has warned there is currently no evidence that people who have recovered from Covid-19 and developed antibodies will be protected against re-infection.
Prof Newton told BBC Breakfast today: "We're optimistic that we will have a good antibody test when we need it, which of course is a little later in the progress of the pandemic.
"Not many people would test positive for an antibody test if we had one now, so antibody tests come a little later."
Pressed on when this might be, he said: "The people who are developing it are talking about having tests available for the end of May, early June.
"But there are antibody tests available now, it's just that we think there's potential to get a better antibody test, and we're not rolling out an antibody test until we've got those."
Earlier in the outbreak, the Government bought millions of antibody tests in the hope they could be rolled out into the community.
But Downing Street later said it would seek refunds from companies that were unable to improve the failed antibody tests.
