Ieuan Wyn Jones said Labour was unable to handle the economic crisis
Plaid Cymru leader Ieuan Wyn Jones has accused Prime Minister Gordon Brown of presiding over a government that has seen "the poor pay more".
In his party conference speech in Aberystwyth, he accused Labour of abandoning its principles and being unable to handle the economic crisis.
He said Plaid reacted decisively to the downturn as Labour's coalition partner in the Welsh Assembly Government.
Mr Jones also renewed his call for a Welsh parliament.
Mr Jones, who is is deputy first minister and economy and transport minister in the assembly government, told delegates that Plaid in government had been "quick off the mark" in responding to the economic crisis.
By contrast the Labour administration in Westminster had "dithered", he said.
There'll be no hiding place for Welsh Labour MPs who say one thing in their constituencies and another in their cosy club atmosphere of Westminster
Ieuan Wyn Jones, Plaid Cymru leader
"We've seen thousands of people in Wales fall into fuel poverty, thousands likely to lose their homes through mortgage default and most people struggling to meet their household bills as the price of food shoots up," he said.
"Frankly, people have had enough. They want a government in London that not only understands their concerns, but is prepared to do something about it."
He said his party was "doing what they can" to protect Wales from wider economic downturn while Mr Brown and Chancellor Alistair Darling had "lost the confidence of the electorate".
He said it was a "scandal" that energy companies were making billions of pounds in profit while so many Welsh households were experiencing fuel poverty.
Mr Jones insisted Plaid were prepared for a general election and called on delegates to campaign like never before to return more Plaid MPs to Westminster.
Plaid Cymru leader Ieuan Wyn Jones says his party is ready for a general election
However, he reserved his fiercest attacks for Labour MPs, rather than Labour assembly members who make up the majority of the ruling coalition in the Senedd.
"Labour MPs have let us down," he said.
"There'll be no hiding place for Welsh Labour MPs who say one thing in their constituencies and another in their cosy club atmosphere of Westminster."
There was also questioning but not direct criticism of the Conservatives' position on devolution.
"Where do the Tories now stand on devolution?" he asked.
"They have a devolutionist wing, but are they strong enough to force [David] Cameron to back plans for more powers for the assembly?"
As for Plaid's stance, Mr Jones again called for a full law-making parliament for Wales.
He said: "We're discovering a new sense of confidence in ourselves - our new Welsh agenda.
"An Agenda which allows us to believe that we can reach our full potential without playing second fiddle to the priorities set in London."
However, there was no mention of the referendum required to make further powers for the assembly a reality.
According to the One Wales coalition agreement between Plaid Cymru and Labour, a referendum must be held on or before the next assembly election in 2011.
But Mr Jones hinted at the tensions that exist between some in the two parties, telling the conference that Welsh Labour MPs "don't want to see more powers for the assembly."
Mr Jones' speech was warmly received by delegates, who earlier voted overwhelmingly to make opposition to the proposed Severn barrage official Plaid policy.
This appears to be at odds with the party's commitment in the One Wales agreement with Labour, which states the coalition's "support for a study on the proposed barrage, including its environmental impact".
The feasibility study into the barrage was announced in January and is not expected to conclude until 2010.
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