Mr McConnell retained the seat last May with a majority of almost 6,000, but a swing of nearly seven per cent went to the SNP.

However, Mr McConnell last week admitted to the House of Commons foreign affairs committee that he might not take up the position of High Commissioner to the Republic of Malawi for 12 months after the role becomes available in January.

Now SNP Central Scotland MSP Christina McKelvie claims Labour are just trying to avoid a by-election.

She said: "That Labour is running scared of a by-election in one of their strongest constituencies shows just how much Scotland has changed in the last 12 months.

"Support for the SNP has continued to increase as people across Scotland see the strong record of delivery from Alex Salmond and this SNP Government.

"Unless he is planning a leadership comeback, Jack McConnell is merely marking time in Holyrood until Gordon Brown has the courage to call an election."

Her claims were echoed by SNP business convener and Westminster leader Angus Robertson MP who said: "Jack McConnell has been caught on the hop by the foreign affairs committee.

"If Brown hadn't botched the election last October Mr McConnell would be long gone.

"There is no doubt that Labour are scared of a by-election at a time when the SNP are riding high in Scotland.

"It is frankly unacceptable that our neutral diplomatic service should become politicised in this way."

The current High Commissioner to Malawi, Richard Wildash, ends his term in January and last August former First Minister Mr McConnell was nominated by Prime Minister Gordon Brown to take over.

Mr Brown said: "I believe that he will make an excellent representative of the United Kingdom Government in Malawi and I am pleased he has accepted the Government's offer of the position of High Commissioner to Malawi, after the present High Commissioner completes his posting and at an appropriate moment."

Mr McConnell says he has no say in when he will take the job and accused the SNP of not understanding the issue.

He said: "Yet again the SNP are trying to create a political bandwagon to jump on. If they understood anything about the diplomatic service they would not make such ridiculous points.

"Until the Foreign Office want me to start my new post, I will continue to fight for my constituents.

"The SNP are trying to de-prioritise Ravenscraig. They have dropped support for town centre regeneration and they want to kill off the new Wishaw health centre.

"They might not like it, but I will do all I can to protect this constituency from the actions of the SNP Government."