Wales' health secretary has rebuked Betsi Cadwaladr University Health Board for "indefensible" delays to official NHS Wales performance statistics.

Jeremy Miles criticised a lack of urgency from the health board, pledging to launch a formal investigation into data standards and governance if issues are not resolved in 24 hours.

During topical questions in the Senedd on Wednesday, Plaid Cymru's Mabon ap Gwynfor warned of a "fundamental failure" with latest NHS statistics which were partially published last week.

Mr Miles told the Senedd the latest stats were postponed due to data quality issues, relating to referral to treatment waiting time data at the north Wales health board.

The health secretary pointed out that a partial statistical release, which covered areas usually published other than referral to treatment, was issued the next day.

'Tip of the iceberg'

"We are working with the health board to urgently address the issues," he said.

Mr ap Gwynfor warned the delay was "just the tip of the iceberg" when it comes to shortcomings in the quality, consistency and transparency of health data in Wales.

He said: "It's disappointing that instead of being upfront from the outset about the precise cause of this problem, we've had to put forward this topical question to try to get transparency and understand what on earth is going on."

Plaid Cymru's shadow health secretary pointed to comments from Iona Collins, chair of the British Medical Association Cymru, who warned long waiting lists are being "obscured".

Mr ap Gwynfor explained waiting times in Wales only reflect the period after a hospital's receipt of a referral, unlike in England, rather than when GPs make a referral.

He also warned statistics may be "downplaying" pressures on specialisms such as orthopedics. "We deserve transparency and clear, unambiguous answers," he said.

'Indefensible'

Calling for a comprehensive audit, Mr ap Gwynfor asked whether a contentious decision to publish provisional NHS data ahead of official statistical releases contributed to the problem.

The health secretary replied: "The situation to which the member refers is indefensible and I don't seek to defend it – we're all entitled to rely on the timely reporting of accurate data."

Mr Miles held a public meeting with the health board last week and questioned the delay. "There's been no attempt whatsoever not to address the question," he said.

He said the NHS Wales chief executive and his officials have been in constant contact with the health board to seek to understand the cause of the issue.

He stressed: "Official statistics are produced independently, free from political influence or ministerial decision, and they adhere...to a range of codes of practice..."

"What I will say is that less progress has been made than I expected and was assured would have occurred by close of business yesterday. I am not at all happy with the level of urgency which the executive team is bringing to resolving this matter."

'Investigation'

Mr Miles, who was meeting the health board's chief executive later that day, told Senedd members he expects the issue to be resolved within the next 24 hours.

"If it is not, I will launch a formal investigation into data standards and governance," he said.

James Evans, the Conservatives' shadow health secretary, pressed his opposite number about the precise cause of the data debacle.

The Brecon and Radnorshire MS raised concerns about a ministerial statement on waiting times being postponed until January as a consequence.

Mr Miles was unable to give a categorical answer to the question of what went wrong but he said: "The incident which triggered the concern originally was around the numbers of people appearing on lists when they had been treated."

He reiterated that he would launch a formal investigation if the issue is not resolved quickly, committing to publishing a written ministerial update later in the week.