The World Health Organisation raised its pandemic alert last night as two people admitted to hospital in Scotland were confiirmed as the UK�s first cases of swine flu.

CAROLYN CHURCHILL and ROBBIE DINWOODIE

The World Health Organisation raised its pandemic alert last night as two people admitted to hospital in Scotland were confirmed as the UK's first cases of swine flu.

As the suspected death toll in Mexico rose to 149 and several cases of swine flu were confirmed in the US, Canada and Spain, the WHO raised the alert status to four - a level that "marks a significant upwards shift in the risk for a pandemic". As a result, the UK Foreign Office later advised against all but essential travel to Mexico.

The two people in Scotland - according to reports a young couple; a man and woman from the Falkirk area - returned from Mexico last Tuesday and sought medical advice on Saturday.

Speaking at her third emergency briefing since the flu scare broke, Health Secretary Nicola Sturgeon said that tests on the two had proved positive but they were recovering well in isolation at Monklands Hospital in Airdrie, Lanarkshire.

A further seven people who had been in contact with them have since developed mild symptoms, Ms Sturgeon said, and they were receiving drugs at home.

The Scottish Government said that NHS boards were "well prepared" to respond to any further suspected cases and it already has "significant" stockpiles of Tamiflu and Relenza, two antiviral drugs that had been effective in treating cases of the H1N1 strain of swine flu in other countries.

A level-four pandemic alert confirms human-to-human spread of a new virus able to cause community-level outbreaks, but it falls short of warning that the virus has caused outbreaks in two or more countries. The WHO said there were now 73 confirmed cases and 22 confirmed deaths from swine flu worldwide.

Ms Sturgeon said: "I would reiterate that the threat to the public remains low and that the precautionary actions we have taken over the last two days have been important in allowing us to respond appropriately and give us the best prospect of disrupting the spread of the virus.

"However, this is a developing situation which we continue to monitor very closely."

Earlier, Scotland's chief medical officer, Dr Harry Burns, said that it appeared swine flu was not as aggressive as the previous avian flu strain, which had a "very high mortality".

Dr Burns added: "It does seem as if this may turn out to be much less aggressive and virulent than the avian flu strain.

He added: "We need to wait and see what emerges with this one but so far, thankfully, everyone we've seen in North America and New Zealand seems to have had a relatively minor illness."

The European Commissioner advised tourists to postpone non-essential travel to the worst affected areas and US authorities said they were preparing as if swine flu is a full pandemic.

Alan Johnson, the UK Health Secretary, earlier told the House of Commons that there were 25 suspected cases in the UK. Eight cases had proved negative and 14 were undergoing initial investigation.

The figures included a Canadian woman being treated for suspected swine flu in a hospital in Manchester, although a spokeswoman for NHS North West said last night that it was "unlikely" that the patient has swine flu.

Mr Johnson said that there was "understandably trepidation and concern across the world" but added that the UK was one of the best prepared countries to deal with the disease.

The European Union's health commissioner, Androulla Vassiliou, advised people to reassess their travel plans.

"They should avoid travelling to Mexico or the US unless it is very urgent," she said.

Mr Johnson said that the UK Government had put in place "enhanced" port health checks to identify passengers arriving in the UK with symptoms of the illness. Passengers arriving back in the UK on a flight from Mexico were questioned by a doctor before leaving the aircraft at Gatwick Airport.

Bacteriologist Professor Hugh Pennington said that the unknown nature of the swine flu virus may delay the "all clear" from danger.

He said: "It's very difficult to make any predictions when it's not like any flu virus before."