East Midlands Ambulance Service (EMAS) blamed a rise in demand after having the biggest percentage of long delays for serious incidents in the country.
From the start of 2018 to September 2019, 12.8 per cent of calls deemed 'category two' emergencies in the East Midlands took more than an hour to get to, according to a Freedom of Information request by BBC News.
That is the greatest number of long delays for England and Wales' 10 ambulance services, discounting West Midlands and East of England as they did not provide the information.
EMAS director of operations Ben Holdaway said a mixture of an increase in call-outs, A&E attendees and a lack of hospital beds was behind the slow response times.
"These and other factors have combined to mean that in many cases after taking someone to an emergency department, our ambulances haven’t been able to get back on the road quickly and into the community to respond to other 999 calls," he said.
“Every part of the local health and care system wants to tackle these issues, and is working together to do that, but it’s clear that the NHS will need more staff and beds, and a well-functioning social care service, if we’re going to meet the needs of our growing and ageing population over the coming years.”
The BBC revealed the long waits for category one and two 999 calls from January 2018, when a new system of measuring response times came in.
Waits of 60 minutes or more were rare for the immediately life-threatening incidents but an average of one in 16 of the second tier of emergency calls took that long nationally.
The national standard for category two calls is to respond to at least nine out of 10 times before 40 minutes.
Mr Holdaway said there were an additional 75 responses per day experienced during December 2019 and 79 per cent of those were category one or two.
More than 300 clinical staff and 999 call handlers have been hired by EMAS over the last 12 months, he added, and investments have been made in new additional ambulances and other resources.
Also, the service is delivering faster average response times for the most serious calls than two years ago.
But delays at hospitals are taking up a lot of ambulance crews' time - only nine per cent of EMAS' double crewed ambulance hours were available to respond to emergencies in December.
EMAS' figures for category two calls from 2018 to September 2019 were skewed as the longest wait was recorded incorrectly.
In February 2018, the ambulance was recorded as arriving at 11.56pm when it actually arrived at 11.56am, having been called at 11.39am.
While the second-longest wait was for an injury sustained at a nursing home in October 2018, initially deemed a category four call, but was escalated to category two the next day and the ambulance arrived in 13 minutes.