Police described it as "terrifying''.
Election Campaign: Day 3
Labour has warned that a vote for the SNP will help David Cameron back into Downing Street, as the parties ramped up their election campaigning.
Shadow chancellor Ed Balls joined the party's Scottish leader, Jim Murphy, in Glasgow, where he said a vote for the SNP "is a vote to continue Tory austerity".
Earlier, Mr Murphy described the nationalists as Mr Cameron's "little helpers" by targeting Scottish Labour seats and diminishing Labour's chance of forming a government.
A new poll suggests that the prospect of the SNP holding the balance of power at Westminster could also work to Mr Cameron's advantage by convincing voters across the UK to hand him enough MPs to return to power.
Nearly half of voters think SNP influence in the next government would be negative for the UK as whole, a TNS poll of 1,118 adults in Great Britain found.
Just 22% think the SNP would have a positive influence compared with 46% who said it would be negative, the poll for The Herald revealed.
Most voters rejected a formal or informal alliance between Labour and the SNP, with 41% saying neither outcome would be good for the UK.
Mr Balls said: "Every vote in this election that might allow the Tories back in is a vote for continuing austerity in Scotland.
"The only way to end Tory austerity in Scotland is to vote Labour."
Mr Murphy added: "David Cameron can't win seats in Scotland. He has got one constituency in the whole of Scotland, so he needs someone else to win seats for him in Scotland and beat Labour for him.
"And the SNP are playing the role of David Cameron's little helpers."
SNP Westminster leader Angus Robertson said: "Jim Murphy's problem is that Labour were David Cameron's big helpers for two and a half years in the referendum - working hand in glove with them and since then Labour have voted with the Tories at Westminster for more cuts.
"People in Scotland simply do not buy what Labour is saying and repeated polls have shown that people trust the SNP more than Labour to keep the Tories out of government."
Meanwhile, Scottish party leaders were setting out their priorities on law and order at the Scottish Police Federation (SPF) conference at the Trump Turnberry Resort in South Ayrshire.
First Minister Nicola Sturgeon said: "We have proposed modest increases in spending that would help to support our public services, invest in infrastructure and end the damage being done by UK cuts.
"We will argue for a fair deal for Scotland's police service. Police Scotland is the only police authority in the UK unable to recover VAT and is liable to an annual cost of around #23 million. That is money that could and should be spent on frontline policing."
Tory leader Ruth Davidson said her party's key priority would be to scrap automatic early release.
She said: "Nobody understands why a judge's sentence should be immediately slashed the moment a criminal is sent down.
"It has eroded faith in our justice system and it needs to stop."
Mr Murphy said: ''The Labour Party will increase taxes for those who earn more. Anyone earning over £150,000, if Labour wins the election, will have to pay more. Tax avoidance has to be and will be cracked down on.
"We will increase taxes on those who earn most and then it's for people in politics, police officers and families to argue for the police service to get a larger slice of that larger cake because more money would be available."
Liberal Democrat leader Willie Rennie used his speech to criticise the operation of the single police force and said SPF members were right to be frustrated as they had been "let down".
He said: "This Government is focused elsewhere rather than using the powers it has to do the serious job of sorting out the sorry mess it created."
Mr Rennie's Westminster counterpart, Nick Clegg, was also in Scotland on the campaign trail.
More than 100 business leaders signed a letter to the Daily Telegraph backing today's corporation tax cut to 20% and warning that a "change in course" on the economy could hit jobs and investment.
Mr Cameron seized on the letter as support for the Tories' "long-term economic plan" but the Deputy Prime Minister warned that his policies would put the recovery at risk.
Mr Clegg, who travelled to East Dunbartonshire to highlight his party's family-friendly policies including a tripling of paternity leave, welcomed the executives' letter.
He said: "I read the letter carefully. It talks about what this coalition Government has done and I think the signatories to the letter are completely right in saying that about the last thing that this country needs, now that we're emerging from this long shadow of the economic crash in 2008, is a great lurch in one direction or another."
A collision between an aircraft and a drone was only "avoided by providence'', air investigators have reported.
Heart has discovered cases of the so-called 'zombie drug' Spice are being investigated in Scotland for the first time.
Whyte, 46, is on trial at the High Court in Glasgow, where he denies acquiring the club fraudulently in May 2011.
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