The UK Government's legislative response to the Smith Commission on more powers for Scotland falls far short of being a credible bill, a committee of MPs has concluded.
The draft clauses for a new Scotland Bill are "a bit of a guddle", do not meet the brief of the Smith Commission and contain a "legally vacuous" and "potentially contradictory" commitment to enshrine the Scottish Parliament as a permanent institution, a report by the House of Commons Political and Constitutional Reform Committee states.
The committee is also concerned at the haste with which the draft clauses are being enacted.
It recognises the political requirement to fulfil "the vow" of more powers for Scotland quickly, but said this seems to have been at the expense of broader consideration of the consequences for the future of the UK.
The Scottish Government has reaffirmed its demand for the Scotland Bill to be enacted as soon as possible in response to the committee's concerns.
The report states: "The timetable for drawing up legislative plans for the devolution of further powers, which all the three main UK parties signed up to during the referendum campaign, can be seen in retrospect to have been somewhat over-ambitious and impractical.
The result is a set of draft clauses which clearly fall far short of a credible draft Bill and require far more work. Some of them are, as we were told by one witness, 'a bit of a guddle'."
The proposal to make the Scottish Government and Parliament "permanent institutions" contradicts the principle that the UK Parliament is the supreme legislative authority in the UK and cannot bind future governments, and the committee heard it cannot cede powers on a "permanent and irreversible" basis.
However, the committee found that the clause, while "legally vacuous", does "constitute a further political (if not a legal) obstacle to any attempted abolition of those institutions" rendering any future abolition "inconcievable."
The Bill addresses matters of very significant constitutional importance "in a less than satisfactory manner", the committee said.
"Arguably they do not even meet the brief set out in the Smith Commission report, insofar as it can effectively be met under our present constitutional arrangements."
Graham Allen MP, who chairs the committee, said: "Although we recognise the political reasons for the swift publications of draft clauses to give effect to the Smith Commission Agreement, it is disappointing there has been no attempt to provide for full pre-legislative scrutiny of the clauses by this Parliament.
"Following the Scottish independence referendum, a great opportunity to consider devolution across the UK has been missed. It is important that a similar opportunity, when the a Scotland Bill is introduced in the next parliament, is not missed.
"We believe that the next government should establish a mechanism for considering the effects of proposed devolution settlements in the round, together with the trends towards decentralisation in England, to ensure that change strengthens the Union.
"It is worth noting that greater certainty about the constitutional arrangements for the UK could be achieved most effectively by codification of the UK's constitution. With a written constitution, the rules of the game at constitutional moments like this would be clear and transparent, and removed from the realm of political wrangling and uncertainty."
Scottish Deputy First Minister John Swinney said: "We believe that the proposed Scotland Bill should be introduced to Westminster as soon as possible after the UK General Election, in line with commitments made to the people of Scotland. It is for the UK Parliament to then decide arrangements for scrutiny of the Bill at Westminster.
"The Scottish Government supports some of the committee's specific recommendations, notably the need for amendments to strengthen the clause concerning the Sewel convention and the added protection that a written constitution would give to the permanence of the Scottish Parliament.
"We have also put forward to the UK Government a number of proposals to improve the clauses, including the removal of any Westminster vetos."