Kevin Woods said NHS 24 expects 15,000 calls a day this winter

Health chiefs insisted the service was well prepared to deal with these pressures, but said there were some localised shortages of flu vaccine.

They also said that NHS 24 expected more than 15,000 calls a day at peak periods when GP surgeries were shut.

On Boxing Day alone, the telephone advice service expected to take 9,000 calls in the four hours up to 1300 GMT.

The figures were disclosed at a briefing in Edinburgh where NHS Scotland chief executive Kevin Woods and deputy chief medical officer Professor Peter Donnelly set out the NHS's plans.

They said GPs and pharmacists had ordered a total of 1.15 million flu vaccinations in recent months, and the Scottish Executive had ordered a further 75,000 doses as a top-up in case of need.

Winter pressures happen - and this year the cold weather warning means that the NHS may face more pressure than for several years Kevin Woods, NHS Scotland chief executive

Those 75,000 doses would start being distributed within the next two weeks, and the executive had ordered a further 40,000 doses to add to the contingency.

Professor Donnelly said: "You can rest assured we will make sensible and best use of all that we have been able to get hold of."

He said some GPs and pharmacists may have placed their orders early after well-publicised supply difficulties last year.

"Probably what that means is you get more vaccine moving more quickly than the supply chain, and the challenge then becomes evening that out and redeploying it as appropriate," the professor said.

So far, the take-up rate of the flu jabs among the over 65s is about 50%, health chiefs said.

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NHS 24 currently has 260 call handlers and 368 nurse advisors.

During the Christmas and New Year Holiday period all frontline staff will be working on a minimum of six out of the expected eight peak days.

NHS 24 expected to take more than 166,000 calls over the 21 days between 19 December and 8 January. This compared to the 124,000 calls it received in the whole of October.

On December 27 and 28 alone, almost 18,000 calls were expected each day.

The NHS has increased capacity to help cope with winter pressures

Mr Woods said: "There has been a significant increase in overall investment to NHS boards this year and there is increased capacity in the system in terms of beds and staffing.

"NHS 24 and boards have also worked together to improve their capacity to deal with out-of-hours and public holiday calls.

"But winter pressures happen - and this year the cold weather warning means that the NHS may face more pressure than for several years.

"The public can and do play an important part in helping the NHS to ensure that these pressures do not cause significant disruption."