The Lothians MSP claimed a fault in the Scottish Parliament electronic system prevented her vital ballot being counted in the knife-edge vote and tied the outcome at 63-63.
But Holyrood authorities last night issued a statement insisting that the voting system had been checked by officials and was working fine.
Defeat would have committed the SNP Government to talks with other parties about a more enduring overhaul of the council tax, with the SNP’s current proposals for change “undermining the principle of local accountability” according to a motion which was poised to be passed by Parliament before the mix-up.
Furious Labour chiefs have now demanded a full investigation into the episode, but the SNP cheekily hailed Ms Dugdale as the “lone ranger” for saving them from defeat in the crunch vote.
Scottish Labour Business Manager James Kelly said: “Every Scottish Labour MSP voted against the government today. We have complained to the parliamentary authorities.”
Labour insiders last night insisted that Education spokesman Iain Gray, who was sat beside Ms Dugdale, witnessed her press the button to vote.
But a Scottish Parliament spokesman said: “We have checked the voting consoles in the chamber. We are satisfied that the system is working properly.”
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The opposition parties - the Tories, Labour, Greens and Liberal Democrats - had earlier united to change the terms of the initial Scottish Government motion, defeating ministers by a narrow 64-63 margin. When it came to passing the amended version, though, the vote was tied at 63-63 after the omission of Ms Dugdale. Presiding Officer Ken McIntosh, in line with convention, backed the status quo and the motion fell.
But opponents now insist the Scottish Government will have to revise its planned to changes to the council tax
A Scottish Conservative spokesman said: “Notwithstanding the confusion over Kezia Dugdale’s vote, the SNP has been sent a very clear signal that it must rethink its council tax plans.”
The SNP plans, set out in March after a Government Commission found the current system was effectively defunct, involves the creation of new bands. The average band E household will pay about £2 more per week, with those in the highest band paying an extra £10 a week - an average of £517 a year.
Finance Secretary Derek Mackay hinted in a Holyrood debate yesterday that ministers may consider further reform of the council tax system.
Mr Mackay said he was prepared to engage with opposition parties on longer-term change to local taxation. The SNP plans will mean higher charges for some households in order to raise an extra £100 million a year for schools.
Mr Mackay said: “Longer-term change, I think, will need more discussion, consensus and engagement, and I am certainly committed to that through the motion and through the engagement with political parties as we go forward.
“We have embarked on a journey in local taxation. We want to make it more progressive, deliver the steps that we got support for at the elections, then engage further on what can be delivered next in view of the report.”
The changes to the system will mean that Scots are likely to see the first rise in their council tax bills in almost a decade next year.
But Tory finance spokesman Murdo Fraser said the party opposes the approach that ministers are taking in relation to how the increase in council tax will be dealt with.
“Ministers want to create a school attainment fund with money going direct to schools, that’s an ambition that we agree with,” Mr Fraser said.
“But they want to fund this by clawing back from councils that additional money - £100 million that will be raised by these council tax revenues and take this centrally to pay directly to schools. There is absolutely no precedent for what is currently being proposed which undermines both local democracy and local accountability.”
The SNP had previously pledged to replace the council tax with a local income tax when the party won power in 2007, but failed to bring plans before Parliament.
Labour’s Jackie Baillie said: “The SNP promised to replace the council tax but instead they have merely tinkered with.”
The Greens support a land value tax, but spokesman Andy Wightman last night told MSPs in Holyrood there could be a “progressive majority” for a revaluation, with the current system based on property values dating back to 1991.
“We can change,” Mr Wightman said.
“We can, for example, do a revaluation, this is not a complex matter, this is a simple and straightforward matter with modern techniques.”