Pressure was last night mounting on the board of the East of England Ambulance Service after the under-fire trust was found to be failing in a key area by the health regulator.

The Care Quality Commission (CQC) called on managers to produce an action plan within the next seven days after an unannounced inspection concluded the performance of the service had deteriorated over the last 12 months.

The regulator said the NHS trust was failing to deliver when it comes to the 'care and welfare of people who use the service' – the first time this has happened to an ambulance trust – because of slow response times and managers were at a loss as to why performance had fallen.

The chairman of the trust, Maria Ball, pictured below, declined to make a statement to the EDP, which has been campaigning for a better deal for patients and hard-working frontline staff for the last six months.

The CQC said performance against two key standards of reaching 75pc of life-threatening calls within eight minutes and responding to 95pc of A19-category incidents within 19 minutes had deteriorated by about 4pc in Norfolk since September 2012.

'Managers were unable to give us sufficient explanation as to why performance had fallen,' the report said.

The findings of the CQC follow an inspection at the end of January and beginning of February and officials at the region's ambulance service have been told to set out their action plan to improve by March 27.

Andrew Morgan, who has been at the helm of the East of England Ambulance Service since December, said the NHS trust was dealing with an increased number of 999 calls, the ongoing challenge around the handover of patients at A&E departments, and increase in staff sickness. In responding to a list of ten EDP questions, the interim chief executive refused to be drawn on when response times would start to improve and admitted that the 15 extra ambulances announced last month had yet to be fully manned because of staff shortages.

'The trust has already been taking action to address this issue by the ongoing recruitment of more staff, tackling sickness levels, and continuing to work with hospitals to address the ongoing issue of patient handover delays which mean that ambulances are waiting at hospital. Ultimately, we're addressing how to maximise the proportion of resources that go to the front-line.'

Mr Morgan added that the NHS trust was creating new general manager areas – including one for Norfolk and one for Suffolk – to improve services at a local level.

'We've undergone a recruitment drive for 200 more clinicians, which is ongoing and we've got dozens in training or already out on the road. We know that we need more resourcing in Norfolk and Suffolk and with looking at the budget and considering front-line improvements, I expect a good proportion to go to the areas of greatest need,' he said.

However, North Norfolk MP Norman Lamb said he had been promised action plans and improvements by the ambulance trust since October. The health minister added he was awaiting the findings of Anthony Marsh, chief executive of the West Midlands Ambulance Trust, who has been drafted in by the govern-ment to conduct a review of the under-performing service.

Mr Lamb said: 'There has to be leadership to tackle the problems in handover times, making sure staff are inspired and staff have confidence in what they are doing. The board has to be accountable for the performance of the organisation.'

'We have brought in an experienced ambulance leader to identify what has gone wrong and we await his report. It should be concluded very soon and needs to be decisive action to restore the confidence of the public and staff,' he said.

The report by the health regulator said response times to emergency calls were an area of concern following a previous inspection in March 2012 and 'performance had deteriorated during 2012 and that this was particularly evident in the Norfolk area'.

Suffolk Coastal MP Therese Coffey said: 'It is a sad day for the ambulance trust, as it fails on the key measure of response times with the impact on patients and staff. As the first ambulance trust to be failed by CQC on these criteria, board directors, including the chairman, really do have to ask themselves if this is the right time to continue or if they should step aside.

'The problems didn't arise overnight and it will take some time to fix but we cannot wait for a year.'

South Norfolk MP Richard Bacon said: 'There is very poor management and the leadership is lions being led by donkeys and there has to be a clear-out and start-up with a leadership that can command the respect of staff. Other ambulance trusts are facing considerable pressures and are doing a better job.'

The CQC visited the trust's Norwich health and operations centre as part of its inspection. The regulator added that patients had told inspectors that they had been treated respectfully by staff and with professionalism.