Patients began receiving letters over the past week notifying them of changes to their appointments.

It comes amid warnings that the event itself could trigger a fresh spike in Covid cases, piling pressure on an already overstretched NHS.

Health chiefs at neighbouring NHS Lanarkshire - where the majority of non-urgent elective surgeries have been paused since August - have now escalated its risk status to 'Black' and confirmed that a number of cancer procedures will be postponed. These will be rescheduled "as soon as possible", it said. 

One Glasgow patient with Long Covid symptoms who is due to see several specialists told the Herald their face-to-face appointments had been changed suddenly to telephone consultations after months of waiting.

READ MORE: More than 800 Covid deaths in fully vaccinated Scots 

The patient - who did not want to be identified - described the move as "outrageous", adding: "It has been very difficult to get any kind of help or to receive investigations for what are quite concerning symptoms.

"I have been waiting many months for some appointments. I recently had to wait three weeks simply to speak with my GP.

"I have now had two face-to-face appointments switched to telephone consultations. One of these was cancelled by letter and the reason given was 'current health board advice'.

"A telephone consultation is no use to me, nor will it be to so many others on so many waiting lists for so many reasons.

"A two week postponement of crucial meetings with specialists will delay many vital diagnostic tests and could have calamitous consequences.

"So many ill people [are] already waiting such ridiculously long times for investigations and treatment."

After a steep and steady decline in September, Covid cases in Scotland plateaued and are now rising slowly

They added that it was ironic patients were being switched to phone and video appointments to free up roads for climate delegates flying into Scotland who "really should have held their meetings virtually".

Jackie Baillie, Scottish Labour’s health and Covid recovery spokeswoman said the move was a "recipe for disaster". 

She said: “The last thing Scotland’s thinly-stretched health service needs is more disruption. 

“This will come as a fresh blow to patients who have already been languishing on waiting lists for months.  

“There is only so much that can be done through a computer screen and for many of these patients who need to see a specialist, virtual appointments will be all but useless."

Sandesh Gulhane, a Gp, Glasgow Conservative MSP and Shadow Cabinet Secretary for Health, said "measures must be in place to keep traffic moving freely at all times on major routes" during the summit, but that city residents should not "suffer as a result". 

He said: “In some cases, it makes sense for patient appointments to be switched online to reduce unnecessary congestion on Glasgow’s road network.

“But equally there are many where the nature of the patient’s condition makes a face-to-face appointment essential, so there has to be flexibility to ensure Glasgow residents don’t suffer as a result of their city hosting COP26."

NHS Greater Glasgow and Clyde said all urgent appointments and those for cancer patients will go ahead as planned.

In a statement, NHS GGC said: "Ahead of COP26 we are working closely with partners to ensure robust plans are in place to enable us to respond to demands for healthcare during the conference, which includes responding to the temporary increase in population.

"All of our hospital facilities will remain open and operational throughout the conference.

"The Glasgow City transport plan for COP26 requires the city to reduce road traffic substantially ahead of and during the event.

"As part of our contribution to that we have moved face to face appointments to different times and increased virtual appointments. All urgent appointments and those for people with cancer will continue.

"Anyone attending any of our hospitals should plan ahead to avoid disruption."

READ MORE: Claims Scottish Government has 'shifted goalposts' on booster rollout

Earlier this week the health board warned that road closures and the "potential for travel disruption" due to COP26 meant that the public should "plan ahead" and order repeat prescriptions and other essential medication well before the event.

However, Dr Linda de Caestecker, NHS GGC's director of public health, said the health board had worked with primary care colleagues to "minimise any potential disruption" for patients.

In addition to road closures and diversions, members of the RMT union have already voted to strike over pay for the duration of the conference from November 1 until November 12 in a move that would bring ScotRail trains nationwide to a standstill.

Powerful figures, such as Joe Biden, Barack Obama, the Queen and Greta Thunberg, are among the names confirmed to appear at the conference, touted as the world's "last chance" to tackle climate change.

However, there are warnings that the influx of some 25,000 delegates, campaigners and media from around the globe could trigger a fresh spike in Covid cases in the city.

Hotel quarantine rules are being relaxed for some officials arriving from red list countries, meaning that they will only have to isolate for five days instead of the standard 10 as long as they are fully vaccinated.

Despite the scale of the event, attendees will also be exempt from Scotland's vaccine passport scheme.

Professor Devi Sridhar, chair of global public health at Edinburgh University and an advisor on Covid to the Scottish Government, said COP26 was likely to worsen virus rates in and around the city.

She tweeted: “A mass event (with major movement of people in & out) with an infectious virus will cause an increase in cases. While in the case of Covid will put stress on limited health services. Which triggers need for further restrictions.”