East Midlands Ambulance Service (EMAS) is England's worst performing ambulance service, according to newly released NHS figures.
The data shows how many life-threatening calls are responded to within eight minutes, in 75% of cases.
In 2010-11, EMAS's category A response rate was 72.4%, while the average was 74.9%.
An EMAS spokesman said the "extremely disappointing" results were partly caused by the severe weather.
South Central came top with 77.5% but Yorkshire, North West, East of England and Great Western services all fell below the national average.
Ice and snow
EMAS deputy chief executive David Farrelly said in an earlier statement: "There is no getting away from the fact that these are deeply disappointing results for us and for our patients.
"We were hitting the target until the severe snow and ice hit us in the last week of November.
"The prolonged cold spell brought a dramatic increase in patients with breathing problems and flu-like symptoms through December and into January. Unfortunately we were not able to regain our focus through February and March to make up for lost ground."
He said EMAS had a 10% increase in 999 calls in the last year - from 186,643 calls in 2009-10 to 205,248 calls in 2010-11.
EMAS covers Derbyshire, Leicestershire, Rutland, Lincolnshire, Northamptonshire and Nottinghamshire and handles more than 600,000 calls a year.
In 2010, it was ordered to improve after NHS data showed response times had fallen to below the national average level of 76.3%.
EMAS had a response rate of 74.9% for 999 calls in 2009-10.