The Liberal Democrats are to lay strict conditions on any deal with the SNP on local income tax, insisting that variation by local councils be written into legislation.

The Liberal Democrats are to lay strict conditions on any deal with the SNP on local income tax, insisting that variation by local councils be written into legislation.

Party finance spokesman Jeremy Purvis told The Herald ahead of a negotiating meeting today: "Any bill brought forward has to include, on the face of the bill, the ability of councils to vary the rate."

That still leaves open the ability for this to be postponed or phased in at a later date - the Scotland Act, for example, handed down a 3p income tax power that has never been used.

But Mr Purvis wants to stress at this evening's meeting with John Swinney, the Finance Secretary, that he is bringing constructive ideas to the table. "It's the first opportunity to sit down and discuss the issues," he said.

On phasing a deal so that local variation only kicked in several years down the road, he said: "We're willing to be constructive but there should not be any doubt that the power and ability for councils to do it should be there on the face of the bill. We want to be seen as constructive but confirmation on the face of the bill is a cast-iron requirement."

Mr Purvis believes that there are ways of making the SNP proposals far better. For example, he argues that students could be given a minimum income guarantee of £7000, to which an existing tax threshhold would be attached. "The result is that it should be possible to agree to allow all students up to £14,000 before tax," he said.

He also claimed that on dividend income, involving wealthy Scots who may have escaped any contribution, there is a way of ending that loophole, too. He said there was no obstacle to including the necessary data on self-assessment forms.

"I am quite surprised that the SNP have not considered this," said Mr Purvis. He pointed out that for those who asked for specific tax forms to declare extra income there was already one form which the Revenue had created for one tiny grouping - MSPs.

"They've already created a specific form for just 129 people. How difficult can it be to help us have a fair tax for the Scottish people?"