Gordon Guthrie cited his growing disillusionment with the Government's policy on Iraq and the current economic situation for defection to the Scottish National Party.

He formally signed up to the Nationalists as it focused on the international agenda at its conference in Inverness.

Mr Guthrie fought Aberdeenshire West and Kincardine for Labour in the 1999 Holyrood elections and used his computer expertise to construct Labour's electoral software.

If we are to achieve the social and economic reform that are desperately needed, it is patently obvious that we need to move beyond devolution

Gordon Guthrie

Speaking at a press conference organised by the SNP, Mr Guthrie confirmed the two main catalysts in his decision to quit the party were the Iraqi crisis and Scotland's economic performance under devolution.

In particular he blamed Labour's failure to force US President George Bush to abide by United Nations resolutions.

Mr Guthrie also criticised the Scottish economic performance under devolution.

He said: "If we are to achieve the social and economic reform that are desperately needed, it is patently obvious that we need to move beyond devolution."

He said he joined the SNP to play a positive role working within a multi-lateralist Europe.

Strength of argument

Asked about his defection from Labour, he insisted he had been straight with party bosses in Aberdeen.

He said he could be called a "turncoat" but he was not a "scumbag".

SNP deputy leader Roseanna Cunningham welcomed Mr Guthrie's move and claimed it was a "sign of the strength of argument that is winning recruits to the party across Scotland."

She said the party was now winning arguments over Iraq, the economy, public services and social justice.

However, the defection was played down by Labour, with sources describing Mr Guthrie as a local activist and not a major player.

Mr Guthrie's defection came as Alex Salmond - leader of the party's Westminster group - prepared to give his keynote address to the SNP's conference.