More senior figures have left Ukip as the party continues to implode in a row over its association with far-right activist Tommy Robinson.

David Coburn, Ukip’s long-serving Scottish leader, quit on Friday morning, accusing the party of promoting “English nationalism” and anti-Islamic politics.

He was closely followed to the exit door by former leader Paul Nuttall, who said dealing with Mr Robinson was a “catastrophic error”.

The exodus follows the departure of former leader Nigel Farage and former economics spokesperson Patrick O’Flynn in recent weeks.

Gerard Batten, the party’s current leader, sparked outrage among members of the party by appointing Mr Robinson, a former leader of the English Defence League and anti-Islam alt-right social media personality, as an adviser last month.

The party has collapsed in the polls since the EU referendum and has failed to capitalise on its successes.

Mr Coburn, the party’s only MEP in Scotland said in a letter: “As a unionist, I abhor English nationalism as much as I abhor Scottish nationalism. The party has been infiltrated by people with an alternative agenda, which is not the one on which I stood when I was elected and sadly does not represent the values for which Ukip once stood.

“I did not run on an anti-Islam platform. Unfortunately, this seems to be the direction that Ukip is taking – obsessing about this issue to the exclusion of all else at a time when we might lose the Brexit we fought so hard for.”

In a statement, Mr Nuttall, who is an MEP for North West England, said he would serve his term in the European parliament until it expired.

‘Soul-searching’: former Ukip leader Paul Nuttall has also left the party (EPA)

“After much soul-searching over the past week, I have concluded that I must, as of today, resign as a member of Ukip. I do this with an immense amount of reluctance and regret, as I have worked tirelessly for the party for the past 14 years,” he said.

“I am resigning because the party is being taken in a direction which I believe is harmful to Brexit. The association with Tommy Robinson will simply appal many moderate Brexit voters and inevitably be detrimental to the cause.

He added: ”Putting Tommy Robinson front and centre, whilst Brexit is in the process of being betrayed is, in my view, a catastrophic error. To conflate Brexit and Robinson at this crucial moment is to put the Eurosceptic cause in danger and I cannot and will not be party to that.”

Mr Nuttall was Ukip leader for under a year between 2016 and 2017. At the 2017 general election he stood in Boston and Skegness, taking the party from a marginal second place to a distant third place. He was Nigel Farage’s deputy from 2010 to 2016 during the party’s most successful period.

Party leader Mr Batten accused Mr Farage of “sour grapes” for leaving earlier this week, claiming he was “looking for an excuse to walk away for two years and now he’s found it”.

He has appointed Mr Robinson as his adviser on prisons and grooming gangs.

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After marching through central London, there will be a rally on stage in Parliament Square, including speeches from Mayor of London Sadiq Khan. 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AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Demonstrators wave Union and European flags and hold up placards as they pass Trafalgar Square, taking part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Demonstrators hold placards as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit A demonstrator holds a message during a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU. AFP/Getty A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum. PA A historic moment: thousands march to demand Final Say on Brexit Demonstrators take part in the 'People's Vote March for the Future,' in central London, Britain, 20 October 2018. Reports state that the 'March for the Future' is to be led by a column of young people and call for a Peopleâ€™s Vote on the Brexit deal. 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Despite reaching polling highs of around 25 per cent in 2014, Ukip is now back to polling single figures. It has lost other senior members including former leader Diane James, who left in 2016, and Stephen Woolfe, who quit in the same year, branding the group “ungovernable”.