The leader of the campaign against Scottish independence has accused Scotland's first minister, Alex Salmond, of acting like a head of state and abusing the powers of the Holyrood government to silence opponents of independence.

Alistair Darling, the former chancellor who is now leading the Better Together umbrella group of Labour, Lib Dems and Tories against a breakaway, charges the Scottish National party with a nasty campaign of intimidation ahead of September's referendum and says it is exploiting its "power of patronage" to gag institutions, academics and artists who receive funding from the Scottish government.

Alistair Darling. Photograph: David Cheskin/PA

He cited an unnamed businessman who had been set to make "quite a sizable donation" to the no campaign, only to withdraw the offer.

"He rang me up, very apologetically, saying he'd just had a call from someone in the Scottish government who'd got wind of this and who said, 'If you do this, you'll never work for us again,'" Darling told the Guardian.

"We know that people are leaned on. Wherever you go in [Scotland], you get people saying, 'It's been made clear to us that if you're not supporting [independence], say nothing.' They've been going round quangos reminding them that they've got to stay neutral and if they can't support the government policy, they should say nothing. It's just a nasty undercurrent."

Darling added, "You'll find it very difficult to find any Scottish university principals to speak out and when you ask them, they say, 'We've been told not to say anything.' They [the SNP government] are very clear. If you can't support us, you shut up."

He said that threat carried extra force in Scotland, "because the public sector is so big here. A lot of people depend on it." did not name any of those said to have been silenced.

The leader of the no campaign also accuses the SNP of "being quite ruthless about exploiting" the bureaucracy of the Scottish government to advance the Yes cause. He cites a Visit Scotland TV advert, officially aimed at promoting tourism to the country yet shown heavily inside Scotland. It ends with the slogan, "You too can say yes – I was there."

"We know what this is," Darling said. "This is TV advertising for their campaign. And Visit Scotland has been so suborned that they're going along with it."

The former chancellor says the launch of Scotland's Future, the white paper advocating independence, was funded by £800,000 moved from the budget of Scottish Water.

"It's unhealthy that they're able to control so much of Scottish life and they're getting away with it basically. They regard the Scottish government budget as being an extension of their campaign."

In a rare criticism by a politician of an individual civil servant, Darling said, "They're getting away with stuff – we'd have been stopped in our tracks by the civil service. He [Salmond] is very fortunate in his permanent secretary: he's incredibly accommodating." Sir Peter Housden is the permanent secretary to the Scottish government.

But the Better Together leader reserves his most acerbic language for the first minister. Asked if he would be happy to do a TV debate against Salmond, he says: "I will but I don't think he'll do it. Because he's very status-conscious. He regards himself as a head of state. As we say in Scotland, he's got a very good conceit of himself. He's very full of himself."