Sam Oestreicher, Unison national officer for ambulance workers said alcohol-related incidents will put even more pressure on services struggling to cope with wintry weather and an outbreak of norovirus.
He said: 'Ambulance crews and A&E departments are under enormous pressure because of accidents and ill-health brought on by the cold weather, and a major rise in cases of flu and the winter vomiting bug.
'However, that pressure will be at breaking point tomorrow, when office Christmas parties hit their peak…It's hard to believe but it is worse than New Year.'
The London Ambulance Service said that last week was the busiest in its history and services in the North West have also seen record calls.
In London, ambulance workers are handling 1,100 calls about 'life-threatening' situations every day.
According to the service, the status of the problem has been elevated from 'severe' to 'critical' and staff are working overtime, all non-essential meetings and transport have been cancelled and training staff have been put back on the road.
Peter Bradley, national director for the ambulance services and chief executive of the London Ambulance Service said that the entire system was 'struggling to cope'.
'It has been the most difficult 10 days I have seen in the last 10 years. It is absolutely horrendous.'