Italy's anti-establishment 5-Star Movement has voted to cut its ties with the anti-EU UK Independence Party (UKIP) and to hook up instead with the Liberals in the European Parliament.

The move prompted UKIP's former leader Nigel Farage to say 5-Star and its founder Beppe Grillo had sold out and, by teaming up with the "euro-fanatic" Alliance of Liberals and Democrats for Europe (ALDE), had "joined the EU establishment".

Grillo had made the surprise proposal yesterday, saying UKIP had achieved its political goal when Britain voted last year to leave the EU, and maintaining the alliance in the Europe of Freedom and Direct Democracy group now made no sense for 5-Star.

Former UKIP leader Nigel Farage accused 5-Star of selling out. Photo: Shutterstock

Following its credo of direct democracy, it held an online vote of its members in which 78.5 per cent backed his proposal.

Grillo published a letter on his blog, 5-Star's main mouthpiece, expressing his "affection and esteem" for Farage but saying their path had now divided.

If ALDE accepts 5-Star in its ranks, the switch would see the Italian group enter mainstream politics and move away from the anti-system fringes, a shift that might reassure other EU capitals that have grown uneasy about its rising popularity.

5-Star, Italy's main opposition party, rejects traditional left-right ideological labels and so has no natural home among the main political families in the European Parliament.

Its policies include holding a referendum on membership of the euro zone, universal income support for the poor, tax cuts for small businesses and clean energy. It attacks the Brussels establishment but does not want Italy to leave the EU.

Grillo said he had also approached the Greens about a possible alliance, but was rebuffed.

ALDE is led by former Belgian prime minister Guy Verhofstadt, a keen European federalist whose strongly pro-EU views previously have been ridiculed by 5-Star.

An ALDE official in Brussels said the group would meet on Tuesday to decide how to react to 5-Star's move, but the union was likely to go ahead. There had already been "positive feedback" from ALDE members about the proposed tie-up, said the official, who spoke on the condition of anonymity.

Verhofstadt has said he will run for the presidency of the European Parliament later this month and, if 5-Star joins ALDE, he can expect to count on the support of its 17 members.

It remains to be seen what impact 5-Star's move will have on its domestic electoral appeal.

Matteo Salvini, head of the right-wing, euro-sceptic Northern League, also said Grillo had sold out and the League's "doors are open to all 5-Star voters ... who want to continue to fight against this Europe and this euro".

However, consultancy Policy Sonar's head of political risk, Francesco Galietti, said 5-Star's move may make it more attractive to moderates. "5-Star is showing goodwill and making it harder to be dismissed as anti-euro lunatics," he said.