The former First Minister was expected to walk away from Holyrood in 2011 and take up a post as High Commissioner in Malawi.

However, the prospect of a Tory government at Westminster has made that less likely.

There have also been rumours at Holyrood that Mr McConnell is unhappy with Mr Gray’s first year as leader, and may wish to replace him. In recent months, Mr McConnell has steadily rebuilt his profile at Holyrood with well-timed criticisms of First Minister Alex Salmond.

Only last week he reminded the chamber of his work tackling sectarianism and accused Mr Salmond of lacking leadership on the issue.

He has also attacked Mr Salmond’s handling of the troubled Year of Homecoming celebrations, which he initiated in the last administration.

One MSP close to Mr McConnell said the ex-First Minister was deeply unimpressed with Mr Gray, and was quietly eyeing the Labour leadership.

“I’m sure he thinks he could do a better job than Gray. If he thought it was there for the taking, could he resist it?” said the MSP.

However, Mr McConnell’s record as the man who took Labour to its first electoral defeat in Scotland for 50 years will always count against him.

A senior SNP source said: “All of Jack McConnell’s other career opportunities have bitten the dust, but the person who should be really worried is Iain Gray.

“Everyone knows Jack is far better than either of the two people who succeeded him, and he wouldn’t be the first Holyrood leader to make a comeback. I suspect Jack is keeping his options open for when opportunities arise.”

However, a Labour source in Mr McConnell’s constituency of Motherwell and Wishaw said his motives were far simpler. “He loves the constituency and its people. He can walk up Main Street and everyone knows him. I never thought he would walk away in 2011.”

Mr McConnell’s decision emerged after Labour officials asked all 46 of the party’s MSPs whether they intended to stand at the Scottish election, so that alternative candidates could be found.

Only Lord George Foulkes – who had always said he would serve a single term – said he would stand down in 2011.

Kezia Dugdale, his popular Holyrood assistant, is now tipped to replace him on the Lothians list.

At the May 2007 election, when the SNP came to power, Mr McConnell retained his seat with a majority of 5,928 over the SNP.

But he resigned as Scottish Labour leader in August that year, after almost six years in the role, and was replaced by Wendy Alexander, who lasted just nine months in the job. Prime Minister Gordon Brown then named Mr McConnell as High Commissioner to Malawi.

Mr McConnell had fostered relations with the African country, which was discovered by Scottish explorer David Livingstone, and sent public funds to improve its education and health care.

At the time, Mr McConnell was expected to succeed diplomat Richard Wildash in January 2009.

However, amid fears the SNP could win a by-election if he quit Holyrood, Mr McConnell became increasingly vague about the timetable.

Then in October last year his Malawi post was put on hold until 2011, and Mr McConnell was made a “special envoy on conflict resolution” for the Foreign and Commonwealth Office (FCO) instead.

In August this year, the Malawi ambitions took a further knock when career diplomat Fergus Cochrane-Dyet began a three-year stint as High Commissioner and the FCO said it was no longer “automatic” that Mr McConnell would replace him.

Mr McConnell could not be contacted last night but a friend said: “Jack is extremely supportive of Iain Gray’s leadership and the punches he is landing on the Nats, and when he accepted the offer to go to Malawi, he made clear that he would not abandon his constituents in Motherwell and Wishaw.

“He feels he can make a contribution to Scottish politics on issues where he is a renowned expert, like tackling sectarianism, as he did this week.”