A 45-year-old Scottish man is the first person in the UK to have fallen critically ill as a result of swine flu alone - and not because of other underlying health problems.

He is one of two new cases, announced yesterday, which have been admitted to intensive care in Scotland. Neither case is linked to previous clusters of the disease.

The Scottish government yesterday confirmed the new cases were “critical but stable” at the Royal Alexandra Hospital, in Paisley. It also said there had been 23 new cases of the virus in Scotland, bringing the total to 65.

The Health Protection Agency (HPA) yesterday revealed that 61 more people in England were confirmed with swine flu - the largest number announced in one day. This brings the total in the UK to 362.

Neither of the two patients in intensive care has any known links to other cases, to travel or to each other. The other case, a 38-year-old woman from Glasgow, does have previous underlying health problems.

Last week a 37-year-old man, who also had other health problems, was admitted to intensive care at a hospital in Glasgow.

The 57 non travel-related confirmed cases in Scotland now vastly outnumber the eight travel-related cases. There are also 30 possible cases, of which six are travel-related and 24 non travel-related. One case, a relative of the 37-year-old man already in hospital, is described as probable.

Nicola Sturgeon, the Health Secretary, said she understood public concerns over the latest developments.

“In any flu scenario, small numbers of patients will develop complications and will require that kind of medical intervention.

“The fact remains that in the overwhelming majority of cases, people with this virus are experiencing relatively mild symptoms, in some cases very mild.

“We are still pursuing a containment strategy. That means we are still contact tracing for all probable and confirmed cases to try to slow down as far as possible the spread of infection.

“We're getting closer now to a situation where the containment strategy we have been pursuing up until now will evolve into something different. We are now seeing sporadic cases in the community, with clusters taking place around them. Therefore the message to the public is to be vigilant and alert and, crucially, to follow key hygiene advice, which becomes even more important now.

“There is no need for the public to be unduly worried,” she added.

A Department of Health spokesman said: “The localised cases of swine flu found in the UK have so far been generally mild, and we have not seen evidence of widespread community transmission. We are continuing to work to slow the spread of the disease and to put in place arrangements to ensure that the UK is well placed to deal with this new infection.

“But we must not be complacent - it is right to prepare for the possibility of a global pandemic.”

The bulk of the non-travel cases are connected to a cluster in Dunoon, Argyll. A fresh confirmed case has emerged at the town's grammar school, but the pupil was off due to exams when the symptoms emerged and the school will remain open.

Third-year pupils have already been sent home after a pupil tested positive.

Ms Sturgeon added that a primary five pupil in the town's Kirn Primary School has also tested positive yesterday for the virus.

Among the cases in Dunoon was a group of Rangers fans who travelled on a supporters' bus to watch the club's league decider against Dundee United on May 24.

Ms Sturgeon said that some of these supporters had also attended the Scottish Cup Final on Saturday, but added: “The risk of transmission in an environment like a football match is very low. We are now seeing sporadic cases in the community, with clusters developing around them.”

Of the 23 new cases yesterday, 18 of them are connected to Dunoon with further travel-related cases in Lothian and Glasgow.

“I would expect over the course of the ... next couple of weeks, the number of cases to increase significantly,” Ms Sturgeon added.

She will take part in a Cobra meeting today which will discuss possible “refinement” of the government's containment strategy.

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