The former prime minister opened up fresh divisions with the Tories by claiming that they wanted to offer Holyrood full control over income tax because that would allow them to demand a limit on Scottish MPs’ voting rights in the Commons, particularly on budget day.
Brown said this would put the union at risk by cutting Scotland’s links to Westminster.
Cameron repeated at the Conservative party conference in Birmingham that his pledge before Scotland’s independence referendum to fast-track more powers for Holyrood would be honoured in full.
But Brown said the pledge was being threatened by the link to MPs’ voting rights: “In my view, a vow, once written, cannot be casually rewritten or revised.”
He said he had signed a petition on the 38 Degrees website calling on UK party leaders to keep their promises made in the final week of the referendum campaign to swiftly implement new tax and welfare powers.
In a direct attack on the Tory proposals, Brown said devolving all income tax powers to the Scottish parliament would dilute the UK’s collective tax system and undermine the UK-wide remit of Westminster.
Scottish Labour is expected to endorse that stance by insisting that Holyrood should control only about two-thirds of Scottish income tax, when they start talks with Lord Smith’s commission set up by the UK government to devise a common position on further devolution.
Brown saw Smith last Friday for private talks on extra devolution, and gave the crossbench peer a list of 14 additional powers and legal guarantees that he believes would increase Holyrood’s financial and job-creating powers but protect key UK-wide institutions, including collective tax-raising.
Brown wrote in a letter to Labour activists in his Kirkcaldy and Cowdenbeath constituency: “The Tory trap that we are in danger of falling into is to devolve all decisions on Scotland’s income tax rates away from Westminster and then to deny Scotland representation in votes on budget decisions on income tax rates.
“This would be clearly against the material interests of the people of Scotland and put the union itself at risk. They must now demonstrate that it is not true that on the morning after the referendum the Conservative party stopped thinking about Scotland and started thinking only about the Conservative party.”
He added a new demand to the list of powers being sought by Labour for the Scottish parliament, arguing that Holyrood could have the power to spend £4bn of the VAT raised in Scotland on top of Labour’s proposal for Holyrood to control income tax rates up to 15 pence in the pound.
Brown highlighted disputes within the Tories over Cameron’s decision hours after the referendum result was declared to link more devolution with cutting Scottish MPs’ voting rights at Westminster, by citing warnings from the Tory peer Lord Clark about the dangers of rushing into reforms of the Commons.
Implying that Cameron had reneged on a pre-referendum vote deal on more powers by adding in the question on MPs’ powers, Brown said the pre-referendum vow “contained no ifs, no buts and had no conditional clauses and no strings attached and it was not presented as part of wider proposals yet to be unveiled, but as standalone and self-contained.
“To be clear: in my discussions prior to the referendum, no party leader ever suggested that any further caveats, conditions or even considerations would be introduced then or later into the vow.”
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