The Scottish and Welsh nationalists have pledged to continue their close co-operation in parliament after the next election.

Their commitment came as Scottish nationalist leader Alex Salmond made a campaign visit to Wales.

The two parties already co-operate on parliamentary issues, working together in the fourth biggest bloc of MPs behind Labour, the Conservatives and the Liberal Democrats.

They also worked hand-in-hand in the campaign to impeach Tony Blair for "misleading parliament" over the intelligence on Iraqi weapons of mass destruction.

"SNP and Plaid Cymru MPs have taken the prime minister to task at every opportunity for misleading parliament and the people of the United Kingdom, taking us into an illegal war in Iraq," said Salmond.

"It is crucial that we hold him to account for his actions and the SNP and Plaid Cymru are committed to pursuing impeachment in the next parliament."

Plaid Cymru's parliamentary leader, Elfyn Llwyd, said the two parties already "work together extremely well as a team in parliament".

He added that "every additional elected MP will boost our power to stand up for Wales and Scotland on key issues that really matter to our people, such as fair pensions and extra police".

Salmond and Llywd were on Monday hitting the campaign trail in Ynys Mon, where Plaid is seeking to reclaim the seat won by Labour in 2001.

Albert Owen currently holds the seat for Labour, but with a majority of just 800.

The seat is represented in the Welsh assembly by Plaid Cymru's Ieuan Wyn Jones, and the nationalists have drafted in one of their former MEPs, Eurig Wyn, as their parliamentary candidate.