Italy’s parliament has voted to cut the number of representatives in both houses by more than a third.

The lower house approved a law to reduce the number of MPs from 630 to 400 and senators from 315 to 200.

The reform was a manifesto promise of the populist Five Star Movement, the main party in Italy’s governing coalition.

They say it will streamline parliament and save hundreds of millions of euros in salaries and expenses.

However, critics say the move will weaken democracy and increase the influence of lobbyists. The new law is potentially subject to a confirmatory referendum as it makes changes to the Italian constitution.

“It’s done! Promise kept” a blog post from Five Star said after the vote in the lower house on Tuesday.

In a post on Twitter, Five Star said the bill – which was supported by almost all parties – would save the country €1bn (£897m) over 10 years.

“It’s the day we’ve been awaiting forever,” Cabinet Secretary Riccardo Fraccaro said, according to Ansa.

“After almost 30 years of broken promises, the cut in MPs and senators is a reality. A new political season is starting, now the citizens are at the centre.”

The news agency AGI (in Italian) calculated that as an MP costs €230,000 per year and a senator €249,600, the cuts in the lower house would save €52.9m annually and those in the senate €28.7m.

The new law should come into effect after the next elections which are due in 2023.

A governing coalition between Five Star and the far-right League party broke down in August. Last month Five Star entered into a new coalition with the centre-left PD and made the new law a condition of its alliance.

The government’s other main objective is to pass a budget to block a rise in VAT (sales tax), which is set to kick in on 1 January if the government fails to reach its debt-reduction target.