Image copyright Getty ImagesThe coronavirus testing system is struggling to keep up with demand as a growing number of people apply for swabs.
People with symptoms applying for drive-through tests have been directed more than 100 miles (161km) away.
The government says areas with fewer coronavirus cases have had their testing capacity reduced, in order to cope with outbreaks.
But public health experts warn this could miss the start of new spikes.
Although cases are now at a relatively low level, the UK's chief medical adviser Prof Chris Whitty has said he expects containing the virus to be more difficult as we go into winter.
And the return to school and workplaces could lead to even more demand for testing.
The Department of Health and Social Care (DHSC) said it was investing £500m in existing trials of new tests including a rapid 20 minute test and a saliva-based test. These will be trialled on groups of people including staff and students at the University of Southampton and four Southampton schools.
There will also be a trial, in Salford, of the benefits of repeatedly testing a population.
Postcode lottery
A postcode search of the government's coronavirus test booking service reveals:
- People with symptoms living in London are being directed between 50 and 135 miles away, including to testing sites in Cardiff and the Isle of Wight
- A postcode in Devon was directed to a testing centre 109 miles away in Carmarthen
- One in Worthing was directed 40 miles away
- One in Cumbria was sent 50 miles away to Dumfries
- In Sheffield on Wednesday morning the closest available testing centre was 20 miles away
These distances are the ones that are given on the government website, but they appear to have been calculated as the crow flies, rather than being a true reflection of how long it would take to drive - for example, the Devon to Carmarthen route was actually a 206 mile drive according to Google Maps.
National testing capacity has not reduced, but it's already being outstripped by rising applications for tests.
The DHSC has responded by rationing testing slots.
It is prioritising areas with more current coronavirus cases and making fewer tests available in areas with lower prevalence.
Dr Stephen Baker at the University of Cambridge, who has been conducting testing for the area's hospital staff, said this was a "pragmatic move from the government to focus resources where they are most needed", but the strategy could become a problem if more cases developed outside the current areas of concern.
People with symptoms and essential workers can still apply for home kits, although these take longer to return a result.
And it's been taking longer for people who do go to a drive-through testing centre to receive their results back, too.
NHS Test and Trace figures show in the week of 13-19 August, 41% of in-person tests at mobile testing units and drive-through centres gave results within 24 hours. That's down from 61% the week before.
For all routes combined, including home kits, 20% of tests had results back within 24 hours, compared with 29% the week before.
'High demand'
Paul Hunter, a public health expert and professor of medicine at the University of East Anglia, said these issues could act as "big disincentive to being tested" and result in missing local increases "early enough to maybe stop more widespread infection".
A DHSC spokesperson said: "There is a high demand for tests and our laboratories continue to turn test results around as quickly as possible.
"To make sure we stay in control of this virus we are targeting our testing capacity at the areas that need it most, including those where there is an outbreak, as well as prioritising at-risk groups."
But virologist Prof Nicola Stonehouse at the University of Leeds said: "Although cases are low we need to remember that the pandemic started from a single case and that only a small number of people entering the UK (mainly from Italy) resulted in the large number of cases earlier this year."
Even in areas with low prevalence at the moment, "restarting a significant rise in cases is a real risk", she said, as people returned from travelling over the summer and schools reopened.
"The key to controlling the pandemic has to be through testing. And this needs to be made as accessible as possible," she added.
The government has pledged to increase its capacity to 500,000 tests a day by the end of October.
Currently, it says, testing capacity is about 350,000 a day - but only just over half of that is being used.
Daily testing has only broken 200,000 on one day, despite the government hailing reaching its target of having that level of capacity at the end of May.
The DHSC stressed that booking slots were added in the evening for morning appointments and in the morning for afternoon appointments, so more local slots might become available through the day.
The website states: "This service is currently very busy. If you are unable to book a test now or the location and time is not convenient for you, please try again in a few hours when more tests should be available.
"If no tests are available online, do not call helplines to get a test. You will not be able to get a test through the helplines."
Follow Rachel on Twitter
from Via PakapNews