High demand led to slots on offer at only eight out of Scotland’s 56 walk-in test centres when checked on Monday afternoon.
At the same time, of the eight drive-through test sites north of the border only two – Glenrothes and Inverness – had appointments available on the day.
By Monday afternoon, walk-in slots were on offer for the same day at only Wick, St Andrews, Inverness, Kirkcaldy, Dunfermline, Aberdeen Strathdee, Oban and Galashiels.
Other centres showed the message: “There are currently no slots available on this day. Try again this evening, when more test slots will be made available.”
The lack of appointments comes as Scotland recorded its highest number of coronavirus cases since the start of the pandemic.
Provisional data released by the Scottish Government shows 8,252 cases were recorded on Christmas Day, with 11,030 positive tests recorded on Boxing Day and 10,562 on Monday.
For some hours there were no walk-in PCR tests available to book in England on Monday due to a “high demand”, according to the UK Health Security Agency (UKHSA).
However, later on in the afternoon bookings were available in every region, with the UKHSA saying the reduced availability was merely “temporary”.
A paramedic, named Ethan, from Southampton, said he had been “fuming” over initial fears he could miss work after waking up with Covid symptoms.
He told the PA news agency: “I’ve experienced symptoms overnight and into this morning of a new cough meeting the Covid guidelines for requiring a PCR test.
“I’ve tried this morning to book a test locally for which nothing whatsoever was available. I’ve had to book a testing kit with a estimated delivery of two days and unsure of how long it will take results to return back.
“I’m a NHS paramedic and I was due back into work tomorrow to work through into the New Year.
“My trust is already experiencing high staff sickness rates due to stress and other ailments and Covid-19 related illness, and I’m fearing that this delay in me getting results compared to the length of time it would take me to get a drive-through PCR done and the results from that will negatively affect my colleagues and the public.”
Other Twitter users said the lack of availability could affect travel plans, sports fixtures and business appointments.
A UKHSA spokeswoman insisted tests were available and blamed high demand for the issue.
She said: “Appointments for PCR tests are available, but high demand can lead to temporary reduced availability in some areas. More appointments are made available for people to book every afternoon.
“Testing is playing an integral role in keeping people safe and managing the spread of Covid-19.
“We are very grateful to everyone who is following the Government’s guidance and getting tested to protect themselves, their loved ones and their communities.
“Everyone with symptoms or who is directed to get a PCR test should continue to come forward to get a test delivered to their home or at a test site.”
The Scottish Government has been contacted for comment.