A simple blood test that could diagnose long Covid is on the horizon after a breakthrough by researchers in the UK.

Imperial College London scientists found a pattern of rogue antibodies in the blood of a small number of people with long-Covid symptoms.

The discovery, in a study of just a few dozen people that will now be repeated on a larger scale, could help medics create a simple test for use in doctors’ offices.

At present, there is no test for long Covid and relatively little is known about the condition that is estimated to affect millions worldwide. Last week, the authorities in England said about two million people could have long-Covid symptoms.

Prof Danny Altmann, who leads the research team at Imperial College London, said that even vaccinated people could end up with long-Covid symptoms.

He told BBC News that the UK government’s lifting of restrictions in England on July 19 and its plan for society to “live with” the coronavirus had far-reaching implications.

“If we’re heading into a phase of 100,000 cases per day and we’re saying that 10-20 per cent of all infections can result in long Covid, I can see no certainty that we’re not brewing those long-Covid cases, despite having a vaccinated population,” he said.

Imperial researchers compared the blood of dozens of people and discovered so-called autoantibodies that were not present in people who recovered quickly.

The immune system normally uses antibodies to fight disease, but sometimes it turns on itself. Doctors across the world have seen young Covid-19 patients with cytokine storm syndrome, Prof Danny Altmann, who leads the research team at Imperial College London, said that even vaccinated people could end up with long-Covid symptoms.

Imperial researchers hope a simple test could be ready in 6 to 18 months, although the project would have to be increased from its small sample size.

Dr Elaine Maxwell, from the UK’s National Institute of Health Research, told BBC News that the early findings were promising but that it was a “complex condition”. She said that patients could experience a range of long-lasting symptoms after recovering from Covid-19.