A future British government could still dissolve the Scottish Parliament despite a cross-party agreement that it should be "made permanent", according to the peer who brokered a deal to firmly entrench Holyrood in UK law.

Lord Smith of Kelvin, chair of the Smith Commission on Scottish Devolution, admitted that "nothing is permanent" in UK law.

However, he intends to make the Scottish Parliament so deeply entrenched that MPs will suffer "a plague of boils" if they try to dissolve it, he told Holyrood's Devolution Committee.

Lord Smith's final report, which he has called the Smith Agreement, states: "The Scottish Parliament will be made permanent in UK legislation and given powers over how it is elected and run. The Scottish Government will similarly be made permanent."

But SNP MSP Mark McDonald questioned how anyone could create permanence or bind future governments without a written constitution.

Lord Smith said: "The UK law will say that this is permanent - that is our intention.

"Nothing is permanent. I'm told by constitutional experts down in London that you can't actually do it because it is binding future parliaments.

"But we intend this to be written in such a way that a plague of boils or something will break out if anyone in the future ever decides to prorogue, or whatever you call it, this parliament.

"So it will be said in as strong language that it is possible to be.

"But you are absolutely right - nothing is permanent because future governments, democratically elected, can change those things.

"It will be described as permanent in UK law - UK law which of course can be changed.

"But if you knew a way of making it permanent tell me, because that is the will of the Scottish people."

The Smith Commission, which was set up hours after Scots voted against independence in September, recommended Holyrood should be able to set its own income tax rates, with all of the cash earned staying north of the border.

But while the agreement states there should be "no restrictions on the thresholds or rates the Scottish Parliament can set" on income tax, it said all other aspects would remain reserved to Westminster, including the amount people can earn before they start to pay the charge.

The commission also backed the devolution of air passenger duty, suggested a share of cash raised from VAT be assigned to Holyrood, but recommended corporation tax should remain reserved.

Welfare payments including attendance allowance, carers' allowance, disability living allowance - and the personal independence payment which will replace it - should be devolved, it suggested, along with cold weather payments and winter fuel payments.

A range of other benefits and the state pension will remain under the control of Westminster, although the commission said MSPs should be allowed to create new benefits in areas where they have devolved responsibility and should also be able to make discretionary welfare payments in any other area.

Westminster would remain in charge of licensing for all offshore oil and gas extraction under the proposals but Holyrood could get the power to determine if fracking goes ahead in Scotland.

The Commission had the backing of every major Scottish political party but the consensus was shattered within minutes of the launch of the Smith Agreement last week when the SNP declared it does not go far enough and that it will take a package of "improvements" to the electorate at the general election.