Conservative HQ strongly denied the Liberal Democrat charge, insisting the Tories had made a significant move along the devolutionary road and that their leader was “on board” to give the Scottish Parliament greater tax-raising and borrowing powers.

However, it made clear the Conservative Party would produce its own White Paper as a full response to the Calman Commission if it was to win the General Election.

In a statement titled “our commitment to Scotland”, Mr Cameron noted: “We accept the Scottish Parliament needs to have more financial accountability through greater powers over raising and spending taxes and over borrowing.”

Jim Murphy, the Scottish Secretary, hailed the Government’s proposals as a “new deal” for Scotland and insisted greater tax-raising powers would create greater accountability in Edinburgh.

However, the Scotland Office admitted that, under a future Labour government, the earliest the new tax powers could be introduced was April 2012, and they might not be introduced until April 2015.

“We have a four-year window and it would only happen when economic and fiscal circumstances allowed,” a spokesman told The Herald.

The SNP attacked the UK Government for unnecessary delay, insisting it could implement immediately some proposals, like transferring power over airguns.

Michael Russell, the Scottish Government’s Constitution Minister, accused Westminster of playing “student politics”, noting how the White Paper came just days before the Scottish Government’s own proposals for an independence referendum.

The political reality is that the issue of more tax powers for Holyrood and the parliamentary heat generated is all geared to making it a key battle ground at the forthcoming General Election.

In the Commons, Mr Murphy argued that the White Paper would produce “a stronger Scotland in a stronger United Kingdom”.

He told MPs that while Holyrood had been responsible for spending money it would, under the proposals, become responsible for raising some of it too.

“We will give the Scottish Parliament greater freedom but also the responsibility to set the level of income tax in Scotland,” he said.

Under the plan, the UK income tax rate would be cut by 10p in Scotland with a corresponding cut in the annual block grant from the Treasury. To maintain the current budget of £30 billion, Holyrood would have to impose a new Scottish income tax at 10p. This would give it about £4.5bn in spending power. If it wanted more money it could raise this level; a cut would reduce its income.

As well as pledging to transfer other taxes like stamp duty, the Government also backed giving Edinburgh capital borrowing powers – but with serious strings attached.

The Treasury would set the limits while taking into account local council borrowing. Moreover, any borrowing would be financed by “increasing taxation in Scotland above the level of the rest of the UK”, ie, through the new Scottish income tax. “There is no borrowing free lunch,” one Whitehall source noted.

While the UK Government pledged to transfer power on setting speed limits and drink-drive limits, it only agreed “in principle” to transfer power on airguns, as a firm definition of “airgun” has first to be established. Two key Calman proposals on transferring Scottish parliamentary elections and air passenger duty are “under review”.

Ministers said they were in favour of improving inter-parliamentary relations such as setting up a joint committee of MPs and MSPs and seeing the Scottish Secretary address Holyrood, but accused the SNP of blocking these proposals.

David Mundell, the shadow Scottish secretary, made clear the White Paper would not “bind” an incoming Tory administration, which would produce its own proposals.

“Conservatives accept that the Scottish Parliament needs to be more financially accountable, that the devolution settlement needs to be tidied up and that Westminster and Holyrood need to start working constructively together for the good of Scotland and Britain,” he said.

Angus Robertson for the SNP sparked Labour ire when, referring to airgun regulation, he asked what explanation the Secretary of State would give to a parent whose child could have been saved from harm but was not because of London inaction.

Mr Murphy hit back, arguing that it was more difficult to draft and pass laws than to issue a “flimsy press release”.

He then accused Mr Robertson of behaving like a nationalist and not a patriot, saying: “A Nationalist puts the SNP first, a patriot puts Scotland first, and that’s the difference between my party and yours and why, increasingly, Scotland is turning its back on the SNP.”

Alistair Carmichael, the LibDems’ Scottish spokesman, accused Labour of letting the Tories off the hook on tax powers by continuing its “policy of delay”.

He said: “If we get a Conservative government, then the Calman recommendations are dead in the water. The Union could be under more direct threat than it is now.”

A Conservative Party spokesman branded that assertion “rubbish”. He said the Tories would use Calman as their “starting point” but would produce their own White Paper if they won power.