The explosive revelations about 999 calls come on the very day that health watchdogs began inspecting Yorkshire Ambulance Service.

The Care Quality Commission (CQC) is thought to have almost 100 staff involved in a formal inspection of YAS.

Inspectors will be visiting the emergency operations centre at Wakefield, interviewing paramedics and other members of staff about the work they do, as well as talking to other organisations and agencies that work closely with the trust such as the police and fire services.

Members of the public are also encouraged to put forward their views.

The Chief Inspector, Professor Sir Mike Richards, said: “We need to make sure that ambulance services are safe, caring, responsive, effective and well led.

“This inspection will provide people with a clear picture of the quality of their local ambulance service, exposing poor or mediocre service, if it exists, as well as highlighting where the trust provides good and excellent services.

“If you have recently needed to call out an ambulance in emergency, or have experience of using the service – we would like to hear from you.” To provide feedback go online to www.cqc.org.uk/syeyorkshireambulance or write to CQC, City gate, Gallowgate, Newcastle upon Tyne, NE1 4PA.

One union claimed it been concerned for years about Yorkshire Ambulance Service’s manipulating calls to try and meet NHS targets.

Unite, who have been “derecognised” as an official trade union by YAS amid a two year dispute, say they reported the issue to watchdogs the CQC.

The union says its recently launched whistle-blowing website has been flooded with 2,000 contacts from concerned staff and claims 500 letters of concern have been sent by the public to the CQC.

Outspoken Unite rep, Terry Cunliffe, said: “Our members tell us they’ve seen calls downgraded or upgraded, depending on whether they’re going to hit their response time targets.

“This happens on a regular basis – they’re a slave to the government target for Red calls.

“They’ve got the third worst figures in the country.

“Our concern is that it’s affecting patients, they’re putting ambulances in particular areas such as big cities to give them more chance of meeting the targets.

“That causes rural areas, such as around Huddersfield, to have extra long waits.

“We believe some of these delays are causing worse clinical outcomes and in some cases lives to be lost.

“But YAS continue to deny it’s happening.”