Scots trying to book lateral flow tests for home delivery were told there were none available to be posted.
A message displayed on the UK Government website earlier on December 29 has warned there are no “home delivery slots” left while advising people they may still be available from pharmacies and other collection points.
However, the website has now reopened for home deliveries to be ordered.
Meanwhile, warnings have also been issued by pharmacies that supplies are currently “patchy”.
Scotland has reported its four highest daily Covid totals in the last four days with a total of more than 39,000 positive test results.
First Minister Nicola Sturgeon has encouraged Scots to test before mixing with other households during the Christmas and New Year period.
The call and increased social events during the festive season has driven up the demand for lateral flow tests for home delivery, which can also be collected from Covid test sites.
Meanwhile, pharmacies have warned that supplies for people to collect are becoming “patchy”.
Leyla Hannbeck, chief executive of the Association of Independent Multiple Pharmacies, told BBC Radio 4: “Every five minutes, approximately, somebody comes into the pharmacy and asks for tests.
“But unfortunately because of the issues around supply being patchy and inconsistent it means that those who come forward for the test don’t always get it, which is very stressful not just for the pharmacy but also for the patients.”
The UK Health Security Agency has said that it has doubled delivery capacity for lateral flow test kits to 900,000 a day since December 18 due to the increased demand amid rising Covid cases.
Meanwhile, in the north and north-east, the tests were being distributed to Christmas shoppers on high streets while batches were also dispatched to smaller villages.