A MAJOR effort to step up campaigning in Scotland for a Leave vote in the EU referendum has been hit by in-fighting between Brexit supporters.

Vote Leave, which is widely seen as the frontrunner to become the official Out campaign group in the June 23 referendum, will launch its Scottish campaign tomorrow.

But it will not be giving a platform to Labour Leave, the group set up by Euro-sceptic Labour MPs and members.

Instead, Labour Leave has chosen to support a rally in Glasgow on Thursday organised by Grassroots Out – Vote Leave's main rival to become the officially designated Leave campaign organisation.

The snub comes as Vote Leave and Grassroots Out (GO) seek to make their presence felt in Scotland.

George Eustice, the Conservatives' Euro-sceptic fisheries minister, will today visit Peterhead as part of the Vote Leave campaign.

Tomorrow Jim Sillars, the former SNP deputy leader, will use the Scottish Vote Leave launch to call on Nationalists to back Brexit.

GO, meanwhile, has Ukip leader Nigel Farage as the star speaker at its rally on Thursday.

Tensions have surfaced as the two camps compete to become the official Leave campaign.

The Electoral Commission watchdog has until April 14 to name the lead Leave and Remain campaigns, which will then fulfil equivalent roles to Better Together and Yes Scotland in the 2014 independence referendum.

Sources said Labour Leave's backing for GO raised questions over how closely it could work with Vote Leave if the latter goes on to head the Out campaign.

The breakdown in relations could hamper efforts to persuade Scots to vote to leave the EU.

Campaign strategists believe support for the EU is "soft" among many Labour voters and see them as a key target in the campaign.

Labour Leave was originally closely allied to Vote Leave but has now established a Labour GO offshoot working with Grassroots Out.

Both are run in Scotland by Nigel Griffiths, the former Edinburgh South MP.

In the battle to become the main Out campaign, Vote Leave is seen as the 'establishment' grouping.

It is chaired by Labour MP Gisela Stuart and includes in its inner circle Michael Gove, Boris Johnson and the former Labour MP for Glasgow South West Ian Davidson.

The director of Scottish Vote Leave is Tom Harris, the former Labour MP for Glasgow South.

GO, which presents itself as a more populist, grassroots movement, is led by a cross-party group of politicians including UKIP leader Nigel Farage.

Also among the leading figures is former Labour minister Kate Hoey, who joined GO after quitting Labour Leave amid growing tensions between it and Vote Leave.

During his visit to Peterhead today, Mr Eustice will meet fishermen and argue the UK would have a stronger voice in quota talks outside the EU.

Tomorrow, Mr Harris will outline the case for Scotland leaving the EU at a campaign launch in Port Glasgow, when he will be joined by Mr Sillars and businessman Alastair MacMillan.

Mr Farage will head a line-up of seven speakers at GO's rally at Glasgow University on Thursday.

Others include Tory MP and former defence secretary Liam Fox, UKIP's MEP for Scotland David Coburn and Brendan Chilton, a key Labour Leave figure speaking under the Labour GO banner.

They will sign a "Glasgow declaration" pledging to put aside other political differences to work together for a Leave vote.

Mr Griffiths did not respond to messages from The Herald.

But Mr Chilton said: "Labour Leave was originally tied to Vote Leave but we have decided it is better for us to stay neutral.

"Some members of Labour Leave wanted to support GO because it is very much a grassroots movement so we set up a branch of Labour Leave called Labour GO.

"Nigel is still involved with Labour Leave and Labour GO and will be our organiser in Scotland".

Mr Harris brushed aside claims of infighting.

He said: "People are willing to work with other groups because there is an understanding that having completely separate campaigns does not help anyone.

"If people want to help my campaign, that's brilliant."