It has been claimed �35m is needed to put the service right

Plaid Cymru had called the debate in the wake of the resignation in May of the service's acting chief executive.

AMs voted 28 to 26 in favour of an inquiry.

They included Dr Gibbons voting by mistake with the opposition while ex-health minister Jane Hutt failed to vote with Labour.

Dr Gibbons pressed the wrong button to vote for the motion but the presiding officer told him that there was nothing he could do about it.

The debate followed months of turmoil, including the service head quitting after a few months and the failure to meet emergency call-out targets.

Roger Thayne had said "an earthquake" was needed to change the way it worked.

Mr Thayne resigned in May after two months in the post saying 500 lives a year were being lost unnecessarily because of the problems within the service.

He said he had stated that �35m was needed to put things right at a time and was asked to make cuts instead.

Dr Gibbons had argued against the inquiry

Mr Thayne said he could not stay in the job because he felt ashamed and he did not want to be accountable for a service that was failing so badly.

The assembly government has consistently denied calls for an inquiry into the ambulance service to be held in public, saying there were internal investigations going on.

BBC Wales Welsh affairs dditor Vaughan Roderick said there were extraordinary scenes in the assembly chamber in Cardiff Bay on Tuesday after members voted and then realised that the opposition had won the inquiry vote.

Dr Gibbons immediately told Presiding Officer Dafydd Elis-Thomas that he had made a mistake.

But Lord Elis-Thomas said there was nothing he could do to rectify it.

It later transpired that Dr Gibbons' predecessor, Jane Hutt - now the business minister in Rhodri Morgan's cabinet - also failed to vote with the rest of the Labour group.

The voting record shows that Ms Hutt did not vote at all during the final vote on a public inquiry in the Senedd on Tuesday afternoon.

It is imperative that the inquiry starts as soon as possible so the process of restoring public confidence in the service can begin Plaid health spokeswoman Helen Mary Jones

After the vote the Welsh Assembly Government said the motion had been passed and that it would consider how to respond to it.

Mr Gibbons told BBC Wales that in his view, the assembly government would have to press ahead with the inquiry, even though he has argued strongly against it.

Liberal Democrat Jenny Randerson, described the minister's mistaken vote "bungling".

Afterwards, Plaid Cymru's Helen Mary Jones called for the inquiry to start as soon as possible.

"This is good news for patients and ambulance service workers as they will find out what has gone wrong with the service, and what is needed to remedy the situation.