Italian Prime Minister Matteo Renzi lost an important ally yesterday when Silvio Berlusconi’s centre-right Forza Italia party said it had ended its pact with him on institutional and constitutional reforms.

Changing voting rules to ensure a clear winner at elections and more stable government have been a priority for Renzi since he became leader of the ruling Democratic Party (PD) in 2013. He also wants to abolish the Senate as an elected chamber to make lawmaking less cumbersome.

In the face of opposition by parts of the PD he has relied on the pact with Berlusconi to try to get these reforms through Parliament. Forza Italia said Renzi broke the pact by failing to consult with them over the choice of constitutional court judge Sergio Mattarella as the new head of state. Mattarella was elected president by Parliament without the votes of Forza Italia.

Nazarene Pact is broken, frozen, finished

Renzi was widely seen as having won a political victory by uniting his PD over the choice of Mattarella and getting his candidate smoothly through.

However, he has jeopardised Berlusconi’s support for the institutional reforms, which are still before parliament.

Berlusconi’s support was guaranteed by the so-called “Nazarene Pact”, named after the PD’s headquarters in Rome’s Via del Nazareno where Renzi first met the 78-year-old media magnate to plan an electoral reform in January last year. The pact has become the central theme of Italy’s politics over the last year, strongly defended by Renzi in the face of critics on the left of the PD. “The Nazarene Pact is broken, frozen, finished,” Berlusconi’s political adviser Giovanni Toti said yesterday.

Forza Italia later issued a statement saying it no longer considered itself bound by the pact and would judge Renzi’s reform proposals on a case-by-case basis.

Italy’s political scene is as muddled as ever. Berlusconi may change his mind and continue to support Renzi but his party, which is largely hostile to the pact, is in disarray and may not follow his instructions even if he does.

The deputy leader of the PD, Debora Serracchiani, showed no concern over Forza Italia’s announcement, saying: “If the Nazarene Pact is dead all the better, the road to the reforms will be more straightforward.”

But Renzi still has many enemies in the PD who may jump at the chance to undermine his reform efforts.