Anti-independence leader says attacks are unacceptable, and hints at possible move from Westminster to Holyrood

Alistair Darling has urged Yes Scotland to curb a surge of "frankly unacceptable" attacks on the no campaign, including a spate of assaults and the destruction of pro-UK posters and billboards.

The former chancellor told the Guardian that the growing intimidation and targeting of the no campaign by a small minority of the yes camp had "crossed the acceptability line" and needed to be stopped.

"There has been dark aspects on this which need to have a light shone on them," Darling said, accusing yes campaigners of systematically defacing or removing pro-UK placards and billboards in towns such as Inverness, and on major roads throughout Scotland.

Darling, chairman of the pro-UK Better Together campaign, also hinted for the first time he could consider switching his political career from Westminster – where he spent 13 years in the Labour cabinet – to the Scottish parliament after the referendum is over.

After four years outside government, the MP for Edinburgh South West said he had become re-energised about politics by the referendum campaign and was "galvanised" for the final six days of the campaign.

But he was planning to sit down with his family after Thursday's vote and take stock before deciding whether to return to frontline parliamentary politics.

Asked if that could include taking a seat at Holyrood instead of Westminster, Darling said: "Of course it does, but I really need to make this clear, that I have said for two years now that I'm going to decide what I do [after 18 September] and that position has not changed one jot.

"[The referendum campaign] has been a long haul; but one of the good things is I do feel invigorated in a way that I wouldn't have anticipated actually until a few months ago.

"A lot of us in this campaign, we have rediscovered a lot of the energy and the zeal and the fervour that we've always had but I suppose when you're in government you deal with an awful lot of day-to-day stuff. It's really, really encouraging."

Darling added, however, that the last few weeks of the campaign had been alarming, having watched a more sinister tone emerge.

Speakers for the no campaign, such as Jim Murphy, had been assaulted, and the Labour leader, Ed Miliband, had been verbally abused while campaigning, he said.

The mother of a disabled child who spoke at a pro-UK rally was harassed and abused, as was the author JK Rowling after she donated £1m to Better Together.

"It's not surprising that in a campaign like this, when you're fighting for the heart and soul of your country, that passions run high, and it would be extraordinary if they didn't," Darling said.

"But what I think is unacceptable is where a line has been crossed, where people feel afraid to speak out. This has been a feature, it's not just businesses, it's people in the arts world, just individuals scared of speaking out.

"I don't want to live in a country where that sort of a culture prevails; because these habits don't die; because once you see you can keep your opponents out of it, that's something that people clock."

A spokesperson for Yes Scotland said: "There is no place for attacks – be they abuse, graffiti, vandalism or physical assault – in this campaign and we have been at pains to impress on everyone, on both sides of the debate, to treat others with respect at all times."

Darling was asked whether he felt uncomfortable that two controversial groups, the hardline Protestant Orange Order, which is blamed for feeding anti-Catholic sectarianism in Scotland, and the anti-EU party Ukip, were staging pro-UK rallies this weekend.

The Ukip leader, Nigel Farage, was holding an anti-independence event in Glasgow on Friday night, while the Scottish and Northern Irish Orange lodges and loyalist bands were to march through central Edinburgh on Saturday: both groups have been excluded by Better Together for fear they will alienate middle-ground and centre-left voters before the referendum.

Darling said: "In relation to the march tomorrow, that is absolutely nothing to do with us – we've made that very, very clear – because they have absolutely nothing in common with the Better Together campaign, absolutely nothing.

"And as for Nigel Farage, he's got more in common with Alex Salmond than he ever will with us in that Ukip and the SNP both believe in blaming somebody else for our problems and the answer is to jump off the ship and hope for something better.

"So, you know, this is a free country, people can express their views even if you disagree with them, but those two things are nothing to do with us."