The UK Treasury has come under fire after ministers and officials repeatedly snubbed meetings with politicians in Wales and Scotland.
Peredur Owen Griffiths, who chairs the Senedd’s finance committee, said calls for meetings with the UK Government to discuss common interests have been rejected.
Mr Owen Griffiths is part of the Inter-parliamentary Finance Committee Forum which has sought meetings with UK ministers, officials and MPs on the Treasury select committee.
The Plaid Cymru MS for South Wales East said: “Time and time again, we have tried to engage with our counterparts in the UK cabinet.
“This is important because many decisions taken in Westminster affect the spending decisions and policy crafted in Wales.
“Unfortunately, all attempts to engage with Tory ministers in a mature and responsible way have fallen on deaf ears.”
Peter Fox, the Conservatives’ shadow finance minister in the Senedd, criticised Plaid Cymru for “propping up” the Labour-controlled Welsh Government.
The Monmouth MS said: “Might I gently suggest that Plaid Cymru look closer to home, focus on holding the Welsh Government to account on their spending decisions and encourage them to ditch their shared plans to spend £120 million on 36 more politicians.”
Mr Owen Griffiths has joined his SNP counterpart, Kenneth Gibson, in taking a stand by cancelling a joint visit to Westminster to mark St Andrew’s Day on November 30.
He said: “This may be disappointing but it is not too surprising given the disdain with which they treat both parliaments and the people of Wales and Scotland.
“The Tories spend much of their time acting like devolution does not exist.
“When they do acknowledge the existence of the Senedd, it is usually to toss insults or seek to reclaim powers in devolved areas.”
“We may try to reschedule a visit in the future in the event of the Westminster government deciding it wants to grow up and engage in a mature approach to politics.”
Mr Gibson argued that engagement is critical as Westminster controls much of the devolved parliaments’ funding.
He said: “Since March, clerks at both Holyrood and the Senedd have worked hard to secure meetings with Treasury ministers, MPs or officials to discuss areas of common interest.”
The Treasury said: “While we value the role of devolved legislature finance committees, the UK Government is accountable to the UK Parliament for its tax and spending decisions.
“We continue to engage with the Scottish and Welsh Governments as part of the wider operation of their fiscal frameworks.”
John Glen, then-chief secretary to the Treasury, appeared before the UK Parliament’s Welsh Affairs Committee on 5 July to discuss funding arrangements for Wales.
Mr Glen was replaced in the role by Laura Trott in the PM’s reshuffle on November 13.
Peter Fox pointed out that Wales receives £1.20 for every £1 spent on health and education as part of a deal agreed with Mark Drakeford while he was finance minister.
He said: “It’s a pity that Labour made the political decision to shortchange our Welsh NHS by only providing it with £1.05 of that.”
Last week, former Conservative group leader Paul Davies said UK ministers were invited to give evidence to a Senedd economy committee inquiry into post-EU funding.
MSs received written evidence from the UK Government instead.
However, Sir John Whittingdale appeared before the Senedd’s culture committee in his role as the UK’s minister for media, tourism and creative industries in October.