Roger Thayne, the former chief executive of the Welsh Ambulance Trust, says lives are still being lost because the service is so poor.
A former head of the Welsh Ambulance Service says he is shocked at the way it is run, three years after he resigned claiming lives were at risk.
When Roger Thayne quit in 2006, he said "an earthquake" was needed to change the way the service was working.
He has now reviewed progress for BBC Wales' Week In, Week Out programme and said it was "definitely costing lives".
Health Minister Edwina Hart said there were "problems" but said they were working to improve the service.
Mr Thayne quit his post in 2006, claiming the "dire" service was putting 500 lives at risk each year and needed £35m investment.
He catalogued outdated equipment, a history of poor management and delays in getting ambulances to patients, which he said contributed to a "dangerous" service.
The assembly government mistakenly ordered an inquiry into the service, after a voting blunder by the then Health Minister Brian Gibbons.
Mr Thayne returned to Wales at the invitation of BBC Wales for a progress report on Wales' ambulance service.
What I am surprised about is why the Welsh Assembly Government and the people of Wales put up with this
Roger Thayne, former acting chief executive, Welsh ambulance service
He said that what he found shocked him, and on key indicators there had been no progress.
Recent figures showed the service was the worst performing paramedic service in England and Wales again, although the service said performances had markedly improved in the last quarter.
Since 2006 ambulance response times across Wales have failed to improve and four out of every 10 people who call 999 are still waiting too long for emergency help.
Some are being ferried to hospital in the back of police cars and even fire engines.
Within Wales, the new counties of Gwent continue to have the worst urban performance and, in the busiest winter months, 999 response times have deteriorated.
Across Britain's towns and cities, 999 calls should have a response within eight minutes.
Last winter in Newport, Monmouthshire and Torfaen, less than a third saw a paramedic within that time.
In the busiest months, January and December, 999 performance has deteriorated over the last two years.
The staff are doing all they can but there are a number of underlying issues
Health Minister Edwina Hart
In December 2006 and January 2007, 59.1% of 999 callouts met the eight-minute target. In December 2008 and January 2009, the figure was 40.5%.
Mr Thayne said: "I'm shocked. It's no better, probably worse, and is definitely costing lives.
"There was the audit commission report into the ambulance service, there was a Health Inspectorate Wales investigation.
"There were promises from the Welsh Assembly Government to take action but nothing seems to have changed.
"What I am surprised about is why the Welsh Assembly Government and the people of Wales put up with this.
Edwina Hart said she was "very proud" of paramedic staff and had spent a lot of time talking to them over the past year.
She said: "The staff are doing all they can but there are a number of underlying issues. I am not happy with the way in which the service is managed.
"Bullying in some parts of the service is a problem, sickness levels have reduced but are too high because staff are overworked and rotas are not right.
"Performance does fluctuate through the year due to seasonal pressures and the ambulance service and hospitals are working to improve access to unscheduled care, including reducing excessive delays with ambulances handing over patients to accident and emergency departments."
She added that the number of inappropriate calls from the public was "a big issue".
Ms Hart said: "People must play their part too in helping to reduce pressure on the services by considering whether they need to call an ambulance or whether they can be cared for and given appropriate advice by NHS Direct or the GPs out-of-hour services."
Ambulance service chief executive Alan Murray said he was "disappointed to hear comments about lives being at risk - these are inappropriate and will cause unnecessary worry for patients and staff".
He said: "When I was appointed in August 2006, we were getting to just 56% of our most seriously ill patients in eight minutes. The May 2009 figures show that, at 66.5%, the trust is responding to many more such patients within the time standard.
"Under its new leadership, the trust has embarked on a five-year modernisation programme. Now, two and a half years in, performance has shown a steady year on year improvement."
Week In, Week Out is on BBC One Wales at 2235 BST on Tuesday.
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