If most people with a cough or fever request a coronavirus test this winter, there won't be enough tests every day for five months, a study estimates.
Based on normal levels of coughs and fever alone - which are common symptoms of flu and cold - demand will peak in December.
The researchers say current UK testing capacity should be "immediately scaled up to meet this high predicted demand".
A new lab will increase the number of tests processed, officials say.
Combined with new technology and new tests, the government plans to reach 500,000 tests a day by the end of October.
But the capacity of the system is currently much less (about 244,000) and demand has risen, resulting in people being sent hundreds of miles for tests or not being able to order home test kits.
The study, which has not yet been published or evaluated, estimated the number of people with a cough or fever last winter in England and predicted the impact of those people requesting Covid-19 tests this winter.
Coronavirus swab tests are offered to people with one of three symptoms - a new, continuous cough; a high temperature; or loss of smell or taste.
But fever and cough are also common symptoms of other respiratory viruses which are at high levels every winter.
The research team, from University College London, Lancaster University and the Liverpool School of Tropical Medicine, predicted that coughs and fevers would jump from about 155,000 cases a day in August to:
- 250,700 in September
- 445,000 in December
And if 80% of people with coughs or fevers requested a test, daily demand for UK testing would exceed current capacity for five months straight, from October to February.
In December, demand would be highest with about 147,000 tests needing to be processed each day over and above the number that labs are able to process.
Even if 60% of people with a cough or fever requested a test, the system would exceed capacity in December and January, the study predicted.
If only 40% got tested, current capacity could manage to cope with demand.
Dr Rob Aldridge, study author from the Institute of Health Informatics at UCL, said there was a danger that more vulnerable people from poorer areas would be most affected by a lack of testing.
"We want everyone with symptoms to get a test so we have to make it easy and rapid.
"Without increased capacity, we won't be able to identify clusters of cases and won't know when action is required," he added.
The results are based on nearly 900 adults and children keeping track of their symptoms in a diary which was kept for six months.
Out of a total of 585 episodes of cough or fever, there were 431 coughs, 57 fevers, and 97 episodes of both cough and fever symptoms.
The study said the government's ambition to increase swab testing capacity to 500,000 tests per day "must be a priority".
Otherwise, the researchers said, UK testing capacity "could be overwhelmed, leading to failure of the NHS Test and Trace service and an inability to control the further spread of Covid-19",