Cabinet Minister David Davies says ex-civil servant Sue Gray dragged her heels as he tried to uncover public service woes in Wales.
He told The Sun on Sunday he held several meetings with Partygate inquisitor Ms Gray, whose most recent Whitehall role was in relation to strengthening the UK.
He said: “Frankly I had problems with the current chief of staff to the Labour Party in her former guise as a senior civil servant.
“She’s not very keen at all on the UK Statistics Authority being able to demand comparable statistics from the Welsh Labour government as well as from the UK government.”
He went on: “We need to be able to see what’s going on across the whole of the UK so we can learn from each other.”
The claims, denied by Labour, come as ministers reveal how Labour would run the health service.
Long-serving Ms Gray quit her civil service post in March.
She was later told by a watchdog that she needed to wait six months before taking up her job with the Labour leader.
After her appointment, ex-PM Boris Johnson questioned the legitimacy of a Partygate probe by MPs “relying” on the evidence from her original report.
But a second watchdog said there was “no evidence” provided to the committee that her “decision-making or ability to remain impartial was impaired” or decisions favoured her new employer.
Meanwhile, Health Secretary Steve Barclay has told counterparts in the devolved administrations about the need for comparable data across the UK.
He said: “It is important that all our citizens can understand the performance of the health services they are receiving and that we can learn from what has been tried and tested.”
Talks will also be held over helping Wales and Scotland reduce long-term waiting times by getting patients to use health services in England.
Last night a Labour spokesman said: “This is desperate stuff from the Tories.
“The facts are Sue Gray signed the first deal between the UK government and the devolved administrations to agree data should be shared to improve outcomes across the UK.”