Roger Williams MP was speaking at his party's spring conference
The deputy leader of the Welsh Liberal Democrats, Roger Williams MP, has attacked Plaid Cymru as "gutless" at his party's spring conference.
Mr Williams said Plaid acquiesced to Labour demands in the assembly government, where they are in coalition.
He said it was time to restore public confidence in politicians and said MPs should get real about their expenses.
Mr Williams was addressing the conference in Cardiff on Sunday.
"London wants to block new powers at every turn," he said.
"It's one thing for Labour to be timid on devolution... but for Plaid to be so gutless is astonishing."
Mr Williams also said the Conservative party did not understand devolution and he described divisions within the Tory party over full law-making powers for the assembly.
"The Tories just don't get devolution," he said.
"Devolution means that Wales gets to decide for itself. The assembly shouldn't need the permission of London-based Tories to implement their policies."
Mr Williams said devolution in Wales was at a crossroads and the system where the assembly passed its own measures through Legislative Competence Orders (LCO) had not worked.
"The LCO system has been thoroughly discredited... We predicted that the halfway house would lead to half measures and we were right," he added.
The MP for Brecon and Radnor told the conference that attempts by the Liberal Democrats to change the system of MPs' expenses had been rejected in Westminster and it was time to "get real".
"Complete transparency. Rejected. External auditing. Rejected. An end to the John Lewis list. Rejected," he said.
Mr Williams was speaking to delegates at the Angel Hotel in Cardiff as the Liberal Democrats prepared to campaign for the European elections, where they will be fighting for the election of their first-ever MEP in Wales.
"We are the only party that is serious about Europe, and we are the only party that has been serious about the economy," he said.
"We should be confident - it's Labour and the Tory ideas that have been thoroughly discredited."
A Plaid Cymru spokesperson said the Liberal Democrats had turned down the opportunity of being part of a coalition government, while Plaid was "getting on with the job" with the powers and system in place.
"With that in mind, isn't it rather ironic that they now label anyone else as gutless?
"The Welsh public will have seen that it's completely pointless to vote for the Lib Dems - the party that chooses not to implement its policies."