An unprecedented number of extra police have been deployed in parts of the UK in anticipation of violence as voters go to the polls for the European elections.

The plan, revealed by Police Scotland, follows an increasingly tense and hostile election campaign that has seen clashes between far-right activists and anti-racism protesters.

Deputy Chief Constable Will Kerr, of Police Scotland, said four units comprising about 100 public order officers would be "strategically placed" throughout the day.

He said: "We would never normally need that sort of support, particularly for European elections.

"We do now. The tone is just fundamentally different."

Milkshaking: New tactic emerges in fight against far-right Show all 6 1 /6 Milkshaking: New tactic emerges in fight against far-right Milkshaking: New tactic emerges in fight against far-right Newcastle says "no thanks Farage" Brexit Party leader Nigel farage is led away by security after being hit with a milkshake at a campaign event in Newcastle Reuters Milkshaking: New tactic emerges in fight against far-right Tommy Robinson covered in a milkshake... While out on the campaign trail for the European Elections in Warrington, a man threw a milkshake in Tommy Robinson's face. Frame 1: Man throws milkshake. Frame 2: Robinson and Co. beat man. Frame 3: Robinson covered in milkshake @AzTheBaz/Twitter Milkshaking: New tactic emerges in fight against far-right ...the day after being covered with a milkshake The day before in Bury, a suspected child threw a milkshake over Robinson before running away Paul Ryder/Youtube Milkshaking: New tactic emerges in fight against far-right Gerrard Batten's image Amy Thompson from Plymouth greeted the Ukip tour bus by throwing a milkshake over the image of leader Gerrard Batten McCoys Media/SWNS Milkshaking: New tactic emerges in fight against far-right Carl Benjamin milkshaked Ukip candidate Carl Benjamin aka Sargon of Akkad was met with a milkshake while campaigning in Totnes, Devon PA Milkshaking: New tactic emerges in fight against far-right Aftermath The remains of the milkshake that struck Carl Benjamin Cornwall Live/SWNS

Police in London said they would be revealing any extra measures in an announcement later on Thursday.

In a sign of how seriously police are treating threats of violence linked to the EU election, Sadiq Khan was given round-the-clock protection after receiving a deluge of death threats in the lead-up to polling day.

The London mayor said his Muslim faith had made him a target in the wake of the 2016 referendum.

At the weekend, officers warned there would be arrests after two police vehicles were damaged during a disturbance at a Tommy Robinson campaign event.

Footage posted on social media showed clashes between supporters of the campaigner, whose real name is Stephen Yaxley-Lennon, and counter-demonstrators in Oldham, Greater Manchester.

On Tuesday, Nigel Farage became the latest European Parliament candidate to have milkshake thrown at him, in a growing protest tactic aimed at right-wing activists.

Nigel Farage hit by milkshake in Newcastle city centre

A day later, the Brexit Party leader was said to have refused to leave his campaign bus after three men armed with milkshakes were spotted in the crowd.

Policing plans for previous elections have tended to focus on preventing voter intimidation and fraud.

During the last European elections in 2014, the government was advised to station police in polling stations in 16 areas at risk of vote-rigging.

At the time, the Electoral Commission raised concerns about voter impersonation in Birmingham, where a judge condemned activities which he said would disgrace a “banana republic” following the exposure in 2004 of systemic postal voting fraud in two wards.

It also named the London borough of Tower Hamlets, where a reporter for The Independent was beaten up while investigating allegations of voting irregularities during the 2010 general election campaign.