To buy time to inform clients about the liberalisation and tweak the market's structure, customers who will not chose a new supplier will be automatically assigned to a provider from July 1, three months later than previously planned, ARERA said.

Customers who still have to pick an electricity contract total around 5 million, while an additional 4.5 million are considered vulnerable and will continue to buy electricity at prices set by ARERA.

Former energy monopolist Enel could lose some of its customers while regional electricity providers including A2A, Iren, Hera and ACEA could get some benefits from the liberalisation, financial analyst said.

(Reporting by Francesca Landini, editing Federico Maccioni)