The commission tasked with brokering a quick deal on Scottish devolution could face calls for a suspension to head off "a very bad botch job", academics and MPs have warned.

The Smith Commission on Scottish devolution is the worst possible forum for constitutional change and is unlikely to emerge with a sustainable solution, MPs have heard.

Tory MP Christopher Chope questioned whether people should rely on the "so-called" devolution vow, as it was given without the UK Parliament's consent and dismissed as "salesman's puff" by nationalists.

And a former Northern Ireland deputy first minister warned that "deals and deadlines" brokered during the Good Friday Agreement led to "implementation failure, stalling and frustration".

Graham Allan, convener of the Political and Constitutional Reform Committee, warned there is a "feeling arising" in some quarters that the Commission should be suspended.

But Scottish Labour chief whip Lewis Macdonald said the powers must be delivered at the pace promised before the referendum.

Professor Michael Keating, director of the Scottish Centre on Constitutional Change, told the committee: "Frankly, I think the timetable that we have been given to do this is not realistic."

He added: "I'm not talking about stringing this out indefinitely and having endless discussion, but at least a year seems to be a reasonable time to put together something that will work and get the technical details right so that it won't unravel and have to be turned to again."

Mr Chope said: "Do you think that there is any chance of that finding favour with the powers that be, rather than this mad rush into a rush job?"

Professor Nicola McEwen, associate director at the Scottish Centre on Constitutional Change, replied: "No, we are in a political context where there is an election round the corner and these create imperatives which mean, I think, that the timetable is not about to be changed.

"I suspect that means whatever comes out is probably not going to be sustainable and we will be back here within a few years talking about either fixing that or 'what next?'."

She continued: "This is not even a convention or a commission where you have got experts and representatives in a room trying to think through and reflect on the issues.

"It's not that at all, it's trying to find agreement between political parties and that is probably the last way I would recommend to nurture consent to an agreement from among the public."

Mr Chope said: "We're heading for potentially a very bad botch job."

Mr Keating said constitutional change "never happens for rational reasons", but he added: "Nevertheless, you can move too rapidly for short-term political considerations and end up making your problem worse because you have created a system that just is not going to work.

"And when we can see that happening I think it is up to us to say 'Hold on a minute, you are creating problems for yourself; that problem will not go away and allow you to move your agenda on - it will come back again very quickly.'

"And I think that's what will happen if we rush through this latest stage of Scottish devolution without proper consideration."

Ms McEwen said: "There's a difference between deliberation and suspension - I don't think anyone is saying we should suspend."

Mr Allan said: "I think some people will say that. I'm sorry for that little intervention there, but I get that feeling arising."

Mr Macdonald said a "small but significant number" of No voters were influenced by the vow and "it is incumbent on the Westminster Parliament to deliver those changes in the way and at the pace that was committed to".

Mr Chope said: "Just to correct the record, those pledges were not made on behalf of the UK Parliament, they weren't even discussed in the UK Parliament. They were not made on behalf of the Government, that was made specifically clear.

"They were just made by the party leaders, and were regarded by the nationalists as being salesman's puff on which nobody should rely.

"So you are saying people did rely on those pledges, so-called? Obviously that's a matter for debate."

Former Northern Ireland deputy first minister Mark Durkan said: "The imperatives of deals and deadlines, from my experience in Northern Ireland, mean that people find themselves either making choices that they later try to resile from.

"Or - and maybe we have seen this with the vow before the referendum - they quickly differ on what the deal that they have made actually means."

He added: "One of the regrets that I have from our process was that, after the high watermark of the referendum in the north and south of Ireland that supported the Good Friday Agreement, the process was too quickly privatised to the politicians, and that is where a lot of the implementation failure, stalling and frustration emerged from."

Mr Allan concluded that it is unrealistic to expect politicians to halt the current political momentum to take a more "rational" academic look at the constitution.

"Politicians have failed to take rational decisions over the last 50 years, and one could argue had they done so there wouldn't have been a referendum in the first place," he said.

"But we are where we are and to ask, after a serious political process, that there is some sort of suspension - with all that that would mean from people who said 'Yes, we told you so, they weren't going to deliver on their oaths' - that is totally unrealistic."