UKIP Scotland's claim to be a credible political force has been questioned after it emerged that the party's democratic decision-making functions had effectively been suspended for nearly eight months.

The right-wing party won a seat at the recent European election, but its Scottish regional branch is still in so-called "special measures" after a bout of infighting.

Ukip, which opposes mass immigration and the European Union, made a breakthrough north of the Border in May when David Coburn became an MEP for Scotland.

However, he was elected against a backdrop of turmoil and division inside his party.

Six of the nine candidates had resigned during the internal selection to pick a candidate, including Scottish leader Lord Monckton and chairman Mike Scott-Hayward, over claims of unfairness in the contest.

The farce prompted UK leader Nigel Farage to fire Monckton by email and triggered Scott-Hayward's resignation.

Paul Henke, another former chairman of Ukip in Scotland, was then suspended for 100 years for speaking to this newspaper. Following a legal challenge, the suspension was lifted.

As a response to this civil war, Ukip seized control of the Scottish party late last year and put it into special measures.

This means an interim decision-making body is imposed and an annual general meeting cannot be held. However, the drastic curb is still in place and no timetable has been announced publicly for its removal.

The Scottish party is currently being run by a committee including branch chairmen.

Despite Coburn's election, Ukip in Scotland is still suffering from infighting.

In an email earlier this month to a party member, Coburn said: "If you spent as much time working for the party as you do carping, Nigel Farage would be padding about 10 Downing Street in his carpet slippers!"

And he added: "You obviously have your own objectives which do not coincide with those of the party and I heartily recommend you consider your position and let the rest of us concentrate on winning elections."

The party member sent back: "If you spent as much time adhering to democracy as you have undermining internal party democracy over the last nine months and centralising power within your small clique … then Nigel Farage wouldn't be getting his inbox filled up with rebuttals of your nonsense!"

He added: "You obviously have your own egoistic objectives which do not coincide with those of a democratic party that belongs to the membership and I heartily recommend you consider your position and let the rest of us who are not five-minute wonders and actually know about Scotland concentrate on winning elections."

Monckton said of the special measures move: "There's a widespread feeling that London have been heavy-handed on this matter, which they kept very quiet during the election campaign.

"It was both unfortunate and unconstitutional."

SNP MEP Alyn Smith said: "Despite the European election result, Ukip remains a negligible presence in Scotland."

A spokesman for Ukip said: "We won a seat in the current situation and the structure is working as well as can be expected."