The Department of Health stipulates that an ambulance should reach 95 per cent of 'Category A' cases - where a person's life is in immediate danger - within 19 minutes.
However, in December four out of England's 12 ambulance services did not manage to reach that figure - double the previous number.
Until then only two were consistently failing to do so - East Midlands and East of England ambulance trusts.
Now North West Ambulance Service and South Central Ambulance Service are on that list as well.
Nationwide, 96.1 per cent of such calls received a response within 19 minutes in December, compared to 96.8 per cent for the eight months from April to December 2011.
Meanwhile, the proportion of Category A cases in which a vehicle was dispatched within seven minutes fell, from 77.1 per cent in November to 74.0 per cent.
A Department of Health spokesman said the increase was due to an increase in demand over the holiday season.
He said: "December saw a greater number of people going to hospital by ambulance than previous months, but despite this, the NHS is still on course to meet its targets by the end of the year."
"Patients should be able to expect a coherent 24/7 urgent and emergency care service which is accessible and safe. We expect all ambulance trusts, commissioners and the wider NHS to look at the data for their region and perform at the highest level."
