Pro-UK campaigners need to set out what new powers would be handed to Scotland if there is a No vote in the referendum, unionist and nationalist business leaders have demanded.

Better Together donor Robert Kilgour, who employs about 650 people in Scotland, told MSPs that he has offered to give the campaign more money if it can come up with a "more positive" manifesto for No but has yet to receive a response.

Clyde Blowers chairman Jim McColl, a Yes supporter, said Better Together had yet to deliver on a pledge he received that they would articulate more powers for Scotland ahead of the referendum.

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Both would support further devolution but their opinions have polarised in the absence of an option to back "devo plus" or "devo max" in the referendum, they told Holyrood's Economy Committee.

Mr Kilgour, chairman of Renaissance Care and chief executive of Dow Investments, said: "I have given Better Together a small cheque, but I told them when I handed it over the three main parties have to come up with a response to the SNP white paper.

"They need to put in writing more positive reasons for Scotland to vote No, all agreed by the three main leaders in London so that they are signed up to no more cuts in the Barnett formula and actually setting out what powers the Scottish Parliament has and what powers it's going to get under the Scotland Act 2012 and in 2016.

"When I gave them the small cheque I said I might consider giving them a little bit more if they said they are putting a fund together for the production of document. I haven't had a response to that to date."

He added: "I am a firm believer in more fiscal powers for the Scottish Parliament. I would like to see it responsible for up to 50% of its budget, whereas I believe it is about 15% just now.

"That would deliver a more settled view and the Scottish people would hopefully be happier to remain in the UK if they had more say on how the money was spent, and therefore not go down the route of wanting independence.

"More fiscal powers in the Scottish Parliament would, in my view, make for more stability and certainty which would allow me to attract more investment and create more jobs."

Mr McColl - whose company employs about 160 of its 6,000-strong workforce in Scotland - told how he had been approached by those campaigning to keep the UK together and had told them they needed to address the issue of more powers for Holyrood.

"I was asked by Better Together, I was invited down to 10 Downing Street to discuss the issues," he said.

But he said he told them if they were going to be "saying 'vote No and we'll do something later', then that is not going to fly".

Mr McColl added: "The answer I got back was: 'You're right, we will need to do something about that'. But I haven't seen anything been done about that."

He told the committee: "To begin with I wasn't pushing for independence, I was pushing for more powers for the Scottish Parliament, more fiscal powers.

"We don't have the powers to attract businesses up here. London is fantastic, it's a huge magnet, there's the infrastructure there.

"We have an opportunity here to get more powers for the Parliament. This isn't an SNP issue, this is an issue to give the Scottish Parliament more powers to decide its own destiny and to run the country in a way that suits Scotland.

"The issues in Scotland are quite different from the issues that face London and the south east, and I think the Parliament needs those powers to address those issues. And the only way to get the additional powers we need is to vote Yes, because there is nothing being put forward by the No campaign.

"It's the status quo and I don't think that hacks it. Doing the same as we've done for the past 15 years for the next 15 and thinking that you're going to get something different, I think is delusional.

"Why any politician in the Scottish Parliament of any persuasion would not want have to more control over what happens in their own nation, it beats me."

The committee also heard from Apex Hotels chairman Norman Springford, a unionist who said he declined a request for a contribution from Better Together as a matter of company policy.

He pledged to remain in Scotland if it votes for independence but said it would impact on his business and investment decisions.

"We will not leave Scotland, we will make good of the legislation that is there, but it will have an effect on the future job prospects of our employees," he said.

He added: "I'm not particularly interested in further fiscal or devolved powers for Scotland. I'm perfectly happy with the union at present and the way the system works."