Undeterred by the pouring rain, a long convoy of motorbikes carrying cheering, flag-waving supporters of Cambodia’s ruling party revved their engines in preparation for their triumphant final rally in downtown Phnom Penh.

People dutifully lined the road as far as you could see, party stickers on their cheeks, the sky-blue hats and shirts they had been given to wear getting steadily wetter.

Perched on the back of a truck, Hun Manet, the 45-year-old eldest son of Prime Minister Hun Sen, greeted the crowds proclaiming that only the Cambodian People’s Party (CPP) was capable of leading the country.

Indeed, his father had made sure that the CPP was the only party which could possibly win the election.

Hun Sen, 70, has run Cambodia in his trademark pugnacious style for 38 years: first in a Vietnam-installed communist regime, then under a UN-installed multi-party system, and more recently as an increasingly intolerant autocrat.

The only party now capable of challenging his rule, the Candlelight Party, was banned from the election on a technicality in May. The remaining 17 parties allowed to contest it were too small or too little-known to pose a threat.

A few hours after the polls closed, the CPP claimed the expected landslide, with a turnout of more than 80%. There were quite high levels of spoiled ballot papers in some polling stations: that was probably the only safe way voters could show their support for the opposition.

With Hun Manet expected to succeed his father within weeks of the vote, in a long-prepared transfer of power, this felt more like a coronation than an election.

“I don’t think we can even call it a sham election,” says Mu Sochua, an exiled former minister and member of the CNRP, another opposition party banned by the Cambodian authorities in 2017.

“We should call it a ‘selection’, for Hun Sen to make sure that his party will select his son as the next prime minister of Cambodia, to continue the dynasty of the Hun family.”

Yet there were signs of nervousness in the CPP before the vote. New laws were hurriedly passed criminalising any encouragement of ballot-spoiling or a boycott. Several Candlelight members were arrested.

“Why was the CPP campaigning so hard, against no one in this election with no real opposition?” asks Ou Virath, founder of the Cambodian think tank Future Forum.

“They knew they would win the election – that was an easy outcome for them. But winning legitimacy is much more difficult.

“They need to keep weakening the opposition, but at the same time, they also need to satisfy the people, so there is no repeat of previous setbacks and disruptions, like street protests.”

Hun Sen is one of Asia’s great survivors, a wily, street-smart politician who has time and again outmanoeuvred his opponents. He has skilfully played off China, by far the biggest foreign investor these days, against the US and Europe, which are trying to claw back lost influence in the region.

But he has come close to losing elections in the past. He is still vulnerable, to rival factions in his own ruling party, and to any sudden downturn in the Cambodian economy which could sour public opinion against him. So as he prepares for a once-in-a-generation leadership change, he is trying to cement his legacy.

A short drive north of the capital, a 33m-high concrete-and-marble monolith was built recently, which he calls the Win-Win memorial.

Its massive base is covered in carved stone reliefs, echoing Cambodia’s greatest historic monument, Angkor Wat.

They depict Hun Sen’s flight from Khmer Rouge-ruled Cambodia to Vietnam in 1977, his triumphant return with the invading Vietnamese army in 1979, and his eventual deal with the last of the Khmer Rouge leaders in 1998 that ended the long civil war – his win-win for the Cambodian people.

Delivering peace and prosperity has long been Hun Sen’s main claim to legitimacy. Since 1998, Cambodia has had one of the world’s fastest-growing economies, albeit from a very low base.

But it is a model of growth which has concentrated wealth in the hands of a few families – the number of ultra-luxury cars on the roads of such a low-income country is jarring. It has encouraged rapacious exploitation of Cambodia’s natural resources and it has left many ordinary people feeling that they are not winning under Mr Sen.

Prak Sophear lives with her family at the back of an engine repair shop, squeezed between the main road and one of the many shallow lakes in the low-lying land outside Phnom Penh. They have been there for 25 years, fishing and cultivating vegetables on the lake.

Today, though, much of the lake has been filled with rubble by a property developer and Ms Sophear’s family have been ordered to leave.

She showed me a document from the local council, confirming how long she had lived there, and another document, a summons to court on a charge of illegally occupying state land. She feels powerless and angry – and she is not alone.

Land disputes are among the most incendiary grievances in Cambodia. All property deeds were destroyed in the Khmer Rouge revolution.

Since the end of the civil war, millions of hectares have been allocated for commercial development, a lucrative arrangement which has made many politicians and businesses allied to Hun Sen very rich.

The courts very rarely rule against these powerful interests. Transparency International ranks Cambodia as 150th out of 180 countries for corruption: in the Asia-Pacific region, only Myanmar and North Korea rank lower.

“Hun Sen always talks about his ‘win-win policy’”, says Ms Sophear. “But we feel it is he alone who wins. We cannot feel at peace, as we now face eviction. We, the real Cambodian people, who live on this land, are suffering in the name of development.”

Those who have tried to campaign against land grabs and evictions have been harassed, beaten and jailed, as have trade unionists and supporters of opposition parties. I asked Ms Sophear how she would vote in this election. “Who can I choose?” she asked. “Who can protect me?”

Half of those eligible to vote are under 35 years old. The CPP has tried attracting them by having Hun Manet and other younger party leaders run this year’s campaign, with a slick social media strategy.

But as most Cambodians have no memory of war or the Khmer Rouge, Ly Chandravuth, a 23-year-old law graduate and environmental activist, says the old CPP campaign points are no longer persuasive.

“Hun Manet’s biggest challenge will be that my generation is very different from previous ones, who were traumatised by the Khmer Rouge,” he says.

“Since I was a child, I have watched the ruling party reminding us of that tragedy, telling us that as they brought peace, we should support them. But that argument is less and less effective. Every time the ruling party brings it up, the young generation mocks them, because they have been repeating it for 30 years.”

Can Hun Manet modify the rough-house, sometimes thuggish leadership style of his father to a softer and more subtle kind of rule? Despite his Western education, his years heading the army and his long apprenticeship, he has never yet held a top political office.

With him, other “princeling” sons of Hun Sen’s contemporaries, such as Defence Minister Tea Banh and Interior Minister Sar Keng, are also expected to replace their fathers in the cabinet – a dynastic shift which keeps the levers of power with the same families, but in less experienced hands. The next few years could be a delicate, even dangerous time for Cambodia.