PLAID Cymru said today it had complained to the broadcasting regulator Ofcom over its exclusion from television debates with the main UK party leaders after Nick Clegg's performance was credited with boosting the Liberal Democrats' opinion poll ratings.

A YouGov poll last night for ITV Wales, conducted after Mr Clegg locked horns with Gordon Brown and David Cameron on television last week, put the Lib Dems on 29%, ahead of Plaid and the Tories and in second place to Labour on 33%.

The Conservatives were third with 23% and Plaid fourth with 9%. When asked last month, 12% said they planned to vote Lib Dem. Labour has dropped four points, Plaid five and the Tories six.

Mr Clegg, who visited Cardiff and Swansea yesterday, has enjoyed wide praise for his appearance on the first General Election leaders' debate, broadcast by ITV last Thursday.

Together with the SNP, Plaid has complained about the decision to leave it out of the series of televised clashes.

Its leader Ieuan Wyn Jones is taking part in debates with Welsh political leaders, the second of which will be shown on ITV Wales tonight.

A Plaid spokesman said the party feared its exclusion could "skew’’ the result of the election, adding: "We think the polls since the debate, and certainly yesterday, show that this is a big danger.’’ Deputy First Minister Mr Jones said Plaid was continuing to press Sky and the BBC for inclusion in the next UK leaders' debates.

The party said at the weekend it was preparing for a potential appeal hearing with the BBC Trust, the corporation's governing body.

Mr Jones said: "I think the real danger now is that the impact of this will be far beyond what anybody expected, although we predicted it would have an impact.

"It doesn't reflect the devolved system in Wales and Scotland.

"We have four parties and one of those parties has been excluded from these debates.

"I think the dynamic of the election has certainly changed. I think everybody accepts that.’’ Plaid is chasing a Lib Dem majority of just 219 in the mid-Wales seat of Ceredigion, which the nationalists lost at the last election in 2005.