The ambulance service covering Portsmouth is spending more than £1m a month for private firms to attend 999 calls.
BBC research shows ambulance trusts across the country paid private companies and voluntary organisations more than £68m to answer emergency calls in the year ended April 2016 - a rise of £46m on the corresponding 12 months four years ago.
The BBC reported that the ambulance service in England took 861,000 emergency phone calls in March 2016, a rise of 24 per cent on the previous year.
To cope with the demand, trusts are increasingly turning to private firms and charities such as St John Ambulance and the British Red Cross.
Martin Flaherty, of the Association of Ambulance Chief Executives, said trusts faced “unprecedented levels of demand” and used private or volunteer services “in support when absolutely necessary... at times of peak demand”.
Of the 11 ambulance trusts which responded to a Freedom of Information request, South Central Ambulance Service - which covers the Portsmouth area - spent the most. Its private contracts cost £13.6m in the year ending April 2016.