A parliamentary by-election prompted by the death of Livingston MP Robin Cook is expected to be held on 29 September.
Robin Cook died after falling ill last month
Labour has been forced to tread constitutional by-ways because the Westminster parliament is in recess.
Formal notice of the former foreign secretary's death on 6 August has been published in the London Gazette.
That allows the Speaker of the Commons to publish the writ for a by-election next Thursday, with a convention of three weeks' notice before polling.
Mr Cook had a majority of 13,000 in May's general election.
Labour is hoping for a bounce from its annual conference in Brighton during the by-election week.
The party will be represented by Mr Cook's former election agent, Jim Devine.
But the Nationalists are relying on disquiet over Iraq, as well as local Livingston controversies, to give them a boost.
Mike Watson has resigned as an MSP
Angela Constance will contest the seat for the SNP, while the Liberal Democrats have chosen Charles Dundas as their candidate and Steven Nimmo will fight for the SSP.
David Robertson will stand for the Scottish Greens, while a spokesman for the Scottish Tories said the party would confirm its candidate early next week.
Mr Cook died last month after falling ill while hillwalking in the Scottish Highlands.
He resigned from Tony Blair's Cabinet in 2003 over the Iraq crisis.
Meanwhile, a Holyrood by-election is pending in Glasgow Cathcart following the resignation of Labour MSP Mike Watson.
He has quit after admitting wilful fire-raising at the Prestonfield Hotel in Edinburgh following the Scottish Politician of the Year awards dinner last November.
The by-election must be held within three months.