Humza Yousaf, the Scottish Health Secretary, said: “We would encourage people, where possible, to [bring forward] an appointment booked.”

One person, who received their second dose four-and-a-half months ago, was told by Prof Leitch on Twitter that they would have no problem getting a booster at a vaccination centre at Glasgow Central Mosque on Wednesday.

However, the venue was one of those to turn away people with appointments, due to the updated guidance not being in place.

Several health boards uploaded urgent pleas to social media accounts for people vaccinated less than 24 weeks ago to stay away. Some people claimed they had received boosters despite waiting less than six months, adding to the confusion.

‘Health boards need to receive the legal instruction’

A spokeswoman for NHS Grampian said: “Health boards need to receive the legal instruction to change how and when medicines, including vaccinations, are administered. This process is underway, but at present we continue to advise everyone to select a booster appointment not less than 24 weeks after their second dose.”

A spokeswoman for NHS Borders said that the new advice “had not been implemented yet” because the health board was waiting on “national protocols which are a legal requirement that we need prior to changing vaccination procedures”.

Alex Cole-Hamilton, the Scottish LibDem leader, said “thoughtful and conscientious people” who had followed advice to get a booster as soon as possible had been let down.

The Scottish Government issued an apology on Wednesday to people who had been turned away and said it had issued instructions to all health boards to vaccinate “in line with the latest advice”.

“Following JCVI advice, clinical and legal guidance requires to be put in place for vaccination teams to implement the changes,” a spokesman said.

“This has been progressed urgently and instructions have now issued to all health boards to vaccinate in line with the latest advice.”