France has begun voting in parliamentary elections which are expected to hand Emmanuel Macron a landslide majority, a second triumph for him after his presidential victory and one which should allow him to embark on sweeping social and economic shakeups.

Just a month after the 39-year-old former banker became the youngest head of state in modern French history, pollsters forecast that his centrist La République En Marche (La REM) party will win as many as 75-80% of seats in the lower house of parliament on Sunday.

Turnout, though, could touch record lows, in a sign of voter fatigue after seven months of roller-coaster campaigning and voting, but also of disillusionment and anger with politics that could eventually complicate Macron’s reform drive.

La REM is barely more than a year old and as many as three-quarters of MPs are likely to be political novices, something which will change the face of parliament at the expense of the conservative and social-democratic parties which have ruled France for decades.

One of the challenges for Macron as he sets out to overhaul labour rules, cut tens of thousands of public sector jobs and invest billions of euros of public cash in areas including job training and renewable energy will be to keep such a diverse and politically raw group of MPs united behind him.

Key rivals say they expect La REM to win a majority and have been urging voters to make the margin as small as possible, saying that otherwise democratic debate could be stifled.

Opinion polls show that voters, while preparing to hand Macron a crushing majority, are actually hoping for a strong opposition to emerge in parliament.

“We need other parties to have some weight,” 54-year-old assembly line worker Veronique Franqueville, who is not a fan of Macron, said in the car park of a tumble-drier factory where she works in the northern town of Amiens. “If he wins it all there will be no debate.”

But among those who plan to vote for La REM candidates the mood is very different, with an overwhelming feeling that Macron needs to be given a strong enough majority to carry out the policies on which he was elected just over a month ago.

“I will vote for the En Marche candidate,” said Aurelie, a 25-year-old nurse in Amiens. “If we want the president to be able to do things we need to give him a majority.”

The election is set to send shockwaves through the older parties, with their unity, and even survival, at stake.

The conservative Les Républicains are expected to be the biggest opposition group in parliament. But polls predict the party will secure no more than 90-95 seats out of 577.

And it may not even stay together. Some Les Républicains MPs could create a separate group to back Macron on a case-by-case basis, while others may see a future firmly in the opposition.

The Socialist party, which governed France until last month, faces a humiliating defeat that could leave it with no more than 25-35 seats.

The election also spells trouble for the far-right Front National, forecast to win between one and six seats when earlier it had hoped to secure a “massive” presence in parliament. Its leader, Marine Le Pen, is expected to be among those who will be elected.

Far-left leader Jean-Luc Mélenchon is also expected to win a seat in parliament. But polls are unclear if his France Unbowed party will reach the 15-strong threshold required to be able to form a parliamentary group.

Polling stations open at 8am (0700 GMT) on Sunday. They close at 6pm in small and medium towns, and at 8pm in Paris and other big cities. At that time, opinion polls will give an estimate of the outcome and official results will start trickling in.