LEGISLATIVE plans for more powers for Scotland fall "far short of a credible draft bill" made at the expense of the implications for the Union, a committee of MPs has concluded.

The timetable for drawing up plans for the devolution of further powers to Scotland can be seen in retrospect to have been "somewhat over-ambitious and impractical", a report by the cross-party House of Commons Political and Constitutional Reform Committee states.

The committee acknowledged that despite attempts by the Bill to the contrary, there were "clearly difficulties" in establishing "beyond doubt" the permanent status of the Scottish Parliament.

It acknowledged the political will to fulfil "the vow" of more powers for Scotland quickly but is concerned that this has been "at the expense of broader consideration of the consequences for the future of the UK".

The committee has said it is "disappointed" there was no attempt to provide for full pre-legislative scrutiny of the clauses by Parliament before its dissolution.

"We call upon the incoming administration to recognise, and consult upon, the consequences for all parts of the UK when introducing legislation to implement the Smith Commission Agreement and other proposals on constitutional reform affecting the Union," said the committee report.

The bill was set out after the No vote in September's independence referendum and Prime Minister David Cameron saying Westminster ministers had kept their promise to strengthen Holyrood. But Scottish First Minister Nicola Sturgeon said UK ministers would get a veto on Scottish powers in key areas.

But the committee said that the bill addressed matters of very significant constitutional importance "in a less than satisfactory manner".

The report states: "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'."

It also says 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".

The report reveals that a clause recognising the Scottish Parliament as a permanent part of the UK's constitutional arrangements was described by Dr Mark Elliott, a reader in public law at the University of Cambridge as "legally vacuous" but that did not mean it was of no consequence.

But the report said Professor Tom Mullen of the University of Glasgow, Professor Aileen McHarg of Strathclyde University and the Law Society of Scotland all argued that the difference in 'draft clause 1' between stating it is permanent rather than that it is "recognised" as such was of "legal significance".

But the committee said it did "constitute a further political (if not a legal) obstacle to any attempted abolition of those institutions".

The committee admitted there are "clearly difficulties in establishing beyond doubt the permanent status of the Scottish Parliament in the UK's constitutional arrangements, given the constitutional principle of parliamentary sovereignty".

But it added: "The political circumstances in which the Parliament could cease existence are at present inconceivable. It is, as the Parliamentary Under-Secretary of State for Scotland told us, 'a prerequisite of our United Kingdom'.

"While draft clause 1, on the permanence of the Scottish Parliament, may seek to recognise the Scottish Parliament and Scottish Government as constitutionally permanent, we doubt whether such a provision would have the effect of making the institutions permanent in constitutional terms.

"A Statute of the Union, or a full written constitution, could provide greater legal certainty over the status of the Scottish institutions, were any further certainty required."

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."