Campaigners against Scottish independence have moved to distance themselves from a planned pro-Unionist Orange Order march through the streets of Edinburgh just days before the crucial referendum vote.

The staunchly protestant Grand Orange Lodge of Scotland is hoping to rally 15,000 supporters in the show of strength on the Saturday ahead of September’s vote.

The spectacle would raise unwanted associations with sectarianism for the No campaign, potentially alienating Catholic voters. Robert McLean, executive officer of the Grand Orange Lodge, told the Sunday Herald that the organisation was in talks with Edinburgh City Council to stage the rally which could see loyalists travel from other parts of the UK to show their support.

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“It’s basically an Orange parade. It’s not just a parade for anyone. You would expect the Orange organisations to come out for a No. We are looking for between 10,000 and 15,000 members in the parade. The majority will be from Scotland but we would expect some of our lodges from Northern Ireland and England to show support,” said Mr McLean.

The Grand Lodge has established its own pro-union campaign called British Together. The organisation has described itself as “fervently opposed” to the idea of Scotland going it alone.

It is understood that the loyal order had offered to work with the cross-party Better Together – the organisation fronted by former Chancellor Alistair Darling – but that the overture was rejected.

Better Together said: “This organisation isn’t part of our campaign and never will be. The best way for people who believe that we are stronger and better together as part of the UK to get involved is by speaking to undecided voters, not marching in the streets.”

Yes Scotland, which is campaigning for independence from Westminster rule, said: “We fully respect that others have a different view and support their democratic right to express it in any legitimate and peaceful way they wish.”

EuroMillions lottery winners Chris and Colin Weir have given a further £2.5m to the independence campaign. The staunch SNP supporters, who gave £1m to Yes Scotland in 2013, are among more than 11,000 backers to pledge money to the campaign.

Figures showed nearly £2.7m has been given in larger donations from seven individual supporters. The disclosure prompted claims by Better Together that Yes Scotland was “almost completely dependent on one source of income”.

The latest poll carried out by Progressive Scottish Opinion revealed a six per cent swing to the Yes campaign in the last six months – confirming a narrowing of the gap between the two camps ahead of the September vote. However, it still put Yes on 34 per cent – 20 points behind No on 54 per cent.

John Curtice, professor of politics at Strathclyde University, said: “On the one hand, the Yes side struggles to win votes if it fails to convince people that independence would be of economic benefit – as many as 50 per cent told Progressive that Scotland would be worse off under independence, while only 31 per cent reckoned they would be better off. On the other hand, faith in the No side is relatively thin.”