THE Unite union plotted against shadow foreign secretary Douglas Alexander by signing up fresh Labour members in his Paisley base in order to install a Unite-friendly rival, party sources have told the Sunday Herald.

The manoeuvres, which included a visit to the area by Unite general secretary Len McCluskey, were allegedly meant to benefit Alexander's fellow Labour MP Jim Sheridan, a Unite stalwart and chairman of its parliamentary group of MPs.

McCluskey recently attacked Alexander as one of Labour's right-wing "Blairites".

Sheridan last night dismissed the claims as "conspiracy theory and speculation", insisting he and Alexander worked well together.

However, senior Labour sources and friends of Alexander said Unite had organised in Paisley to protect Sheridan from boundary changes.

At the time, in 2011 and 2012, Alexander's Paisley and Renfrewshire South seat and Sheridan's Paisley and Renfrewshire North were expected to merge, pitting the two MPs in a head-to-head fight for Labour's candidacy for the new Paisley and Renfrew seat.

Unite ran a membership drive in Paisley, giving it more influence on the candidate selection.

The issue ultimately evaporated because Liberal Democrat MPs withdrew their support for the boundary changes in late 2012, in retaliation for Conservatives MPs blocking reform of the House of Lords.

However, the idea that Unite may have been ready to move against one of Labour's shadow cabinet suggests it has huge ambitions.

Conscious he too had to build his local support, in January 2012, Alexander and the centre-right Community union hosted an "action day" in Paisley, which sources said was interpreted by Unite as him organising against Sheridan ahead of the boundary change.

Despite Sheridan having a huge 15,280-vote majority in the 2010 General Election, Unite made Paisley one of the pilot seats for its strategy programme of getting more working-class MPs elected.

Last September, McCluskey told the union's executive council: "A successful meeting had taken place in Paisley to support Jim Sheridan MP and promote Unite's political strategy."

The minutes of the meeting also revealed the practice of "increasing membership of the Labour Party" was under way in Paisley, a point repeated at the December 2012 executive council.

Three senior Labour members told the Sunday Herald the reason was Alexander and Sheridan gearing up for a boundary battle.

One said: "I know he [Alexander] was concerned. Douglas's people were going into organising overdrive. Unite's organising there was in reaction to Douglas firing the first shot."

Sheridan said Unite's activity was unconnected to boundary changes, despite what others said.

"Unite's political strategy was to get more working-class people involved in the party and politics at every level – MP, MSP, councillor.

"The reason I was picked was that it was something I've been campaigning for for quite some time. I don't think there was any link to the boundary changes or Douglas or anything else.

"I work with Douglas. We work well as a Labour team in Paisley. There's no hidden agenda."

Unite gave £2000 to Sheridan's election campaign at the 2010 General Election. In November 2010, the union spent £6435 sending him on a trip to Mexico "to meet with trade unionists to discuss issues of safety at work and labour relations". And in May this year, Unite spend £2704 to send him on a trip to Toronto in Canada for a conference with trade unionists "under the banner of Workers Uniting".