The day had started badly for Mr Blair after he compared the parliament's powers with those of an English parish council in an interview with the Scotsman, adding: "Sovereignty rests with me as an English MP and that's the way it will stay." His remarks were attacked by the Tories as "ludicrous and patronising," and by the Scottish Nationalist Party's leader, Alex Salmond, who said they exposed the "deceit" of Labour's policy.
Mr Blair was clearly rattled by questions from Scottish journalists on whether Westminster would be able to veto the tax-raising powers of a Scottish parliament. He was unable to answer the question, or others on how the parliament's power would square with his pledge to hold income tax down.
His body language, so assured during the campaign so far, was defensive and he resorted to snapping condescendingly at several persistent inquisitors.
"Look," he said repeatedly and in increasingly exasperated tones, "I have pledged not to raise the basic and top rates of tax in Scotland as well as England and Wales. I can't speak for the other parties; you have to ask them what they would do." It was his toughest grilling so far and it ended with the Scottish press corps declaring themselves unhappy with his answers.
Later Labour's foreign affairs spokesman, Robin Cook, said there would be no veto but that if Labour was elected to control a Scottish Parliament it would comply with the leadership's current tax pledges.
"We can only speak for the Labour Party and we are only accountable for the Labour Party's actions. We will fight that election on a quite clear manifesto that we are not going to raise income tax for the Scottish Parliament in the early years," he said.
The SNP leader, Alex Salmond, claimed Mr Blair had "shown his contempt and derision for Scotland."
"New Labour's devolution policy is now exposed by Blair for what it has always been - a deceit which would return to Edinburgh less power than an English parish council," he said.
John Major was quick to seize the opportunity to attack Labour. Clearly sensing serious vulnerability over the cracks in Labour's campaign, the Prime Minister went on to the offensive in some of the strongest language he has used in the election. "What is clear is their policies are in total and utter chaos as far as Scotland is concerned. They say one thing in England and another thing in Scotland," he said. Earlier, Mr Major had warned of the danger of an English backlash against the Scots. He said that he did not want to see 290 years of Union put in jeopardy.
Jim Wallace, leader of the Scottish Liberal Democrats, said people had a right to decide through the ballot box whether they wanted the parliament to vary taxes. "The tax powers of the Scottish Parliament are every bit as much an issue of democracy as they are of taxation," he said. "Mr Blair is showing more interest in middle England voters than he is in Scottish democracy."