Gordon Brown will have to concede more powers to the Scottish Parliament or pay the high price of seeing the Nationalists gaining ground towards their independence goal, Nick Clegg says.

He gives his warning in an exclusive interview with The Herald ahead of his first visit to Scotland today as the Liberal Democrats' new leader.

He made clear that devolution was "a process and not a fixed state", noting: "Every devolved system of government anywhere in the world shows the first step of devolved power usually leads to others."

Wendy Alexander, the Labour leader at Holyrood, has now joined other political leaders in Scotland to push for greater powers for the Scottish Parliament by setting up a cross-party commission. However, it is known some Labour figures at Westminster - believed to include the Prime Minister - are deeply hostile to it and feel she is dancing to the SNP's tune.

However, Mr Clegg, who represents Sheffield Hallam, thinks the reverse and urges Mr Brown not to set his face against more home rule for Scotland.

"The Labour Party and Gordon Brown would be making a strategic error of significant importance if they were not to understand that by just blocking further progress to devolution you strengthen the hand of the Nationalists.

"I subscribe fully to the idea the best way to address the often highly opportunistic siren call for full independence is to show devolution is a process which is ongoing and not shut the door and in effect say we have gone as far as we want."

Mr Clegg stressed the issue of more Scottish devolution was primarily for Nicol Stephen, LibDem leader at Holyrood, and the "Scottish political class".

However, the LibDem leader made clear that once the commission's recommendations were made - inevitably to seek more powers - and if Mr Brown said no, then Mr Clegg insisted he would seek to "not only remind Gordon Brown but embarrass him too about how it would fly in the face of what some members of his own party in Scotland want".

Speaking minutes after his first appearance as party leader at Prime Minister's Questions, the 41-year-old admitted it was a nerve-racking experience, but also enjoyable. He was greeted with hugs, cheers and kisses in his private office after.

Today, the welcome in from party MSPs and members will also be warm as Mr Clegg visits the Scottish Parliament. As the first non-Scottish LibDem leader for nearly a decade, he intends to visit Scotland regularly.

In his interview, the successor to Sir Menzies Campbell also spoke about his contacts with Mr Brown and David Cameron over constitutional change, claiming that the Westminster system was "on its last legs".

"I said to them: Let's get together as long as we have a no-holds-barred discussion like the terms of the Scottish constitutional convention that led to devolution to Holyrood but that's based on all parties being involved and not just parties talking bilaterally to each other.'"

He added: "If Brown and Cameron are interested in holding cross-party talks along the lines of the Scottish convention, which would really lead to root-and-branch reform of the political system, no one would be more delighted than me.

"But if they're not interested in that and only interested in playing games or picking off one or two issues that would be convenient to them and would ruin the rest, I'm simply not interested in that whatsoever."