The Scottish parliament does not have the power to hold a referendum on independence unless it is given it by Westminster, a Commons committee said today.
The Scottish committee found Holyrood only has control over devolved matters, whereas the union between Scotland and Britain is a reserved matter.
"Any referendum must have an unchallengeable legal and moral basis, to avoid delays and challenges to the legitimacy of the process and its result," MPs found.
"The Scottish government has argued that Holyrood is legally competent to set up a referendum but the committee can find no evidence for this and the Scottish government has provided no legal justification for this view."
The committee, which has no SNP members, also questioned why Frank Mulholland, Lord Advocate and Scotland's chief legal adviser, had not commented on the legality of the issue.
"It is well understood that law officers do not, save exceptionally, make their advice public, but, on a matter such as this, there is a very strong public interest in understanding the legal basis of the Scottish government's approach to a process which will determine the future of the country," it found.
David Cameron has offered to hand legal powers for the referendum over to Holyrood under Section 30 of the Scotland Act, but only if Alex Salmond agreed to an in-or-out referendum without a 'devo-max' option.