Thailand’s Constitutional Court strikes again, removing yet another prime minister from office.

The country’s notoriously interventionist panel of nine appointed judges has ruled that Paetongtarn Shinawatra violated ethical standards in a phone call she had in June with the veteran Cambodian leader Hun Sen, which he then leaked.

In it, Paetongtarn could be heard being conciliatory towards Hun Sen over their countries’ border dispute, and criticising one of her own army commanders.

She defended her conversation saying she had been trying to make a diplomatic breakthrough with Hun Sen, an old friend of her father Thaksin Shinawatra, and said the conversation should have remained confidential.

The leak was damaging and deeply embarrassing for her and her Pheu Thai party. It sparked calls for her to resign as her biggest coalition partner walked out of the government, leaving her with a slim majority.

In July, seven out of the nine judges on the court voted to suspend Paetongtarn, a margin which suggested she would suffer the same fate as her four predecessors. So Friday’s decision was not a surprise.

Paetongtarn is the fifth Thai prime minister to be removed from office by this court, all of them from administrations backed by her father.

This has given rise to a widespread belief in Thailand that it nearly always rules against those seen as a threat by conservative, royalist forces.

The court has also banned 112 political parties, many of them small, but including two previous incarnations of Thaksin’s Pheu Thai party, and Move Forward, the reformist movement which won the last election in 2023.

In few other countries is political life so rigorously policed by a branch of the judiciary.

In this case, it was the leaked phone conversation that sealed Pateongtarn’s fate.

It is not clear why Hun Sen chose to burn his friendship with the Shinawatra family. He reacted angrily to a comment by Paetongtarn calling the Cambodian leadership’s use of social media to push its arguments “unprofessional”.

Hun Sen described it as “an unprecedented insult”, which had driven him to “expose the truth”.

But his decision caused a political crisis in Thailand, inflaming tensions over their border, which last month erupted into a five-day war that killed more than 40 people.

The Thai constitution now requires members of parliament to choose a new prime minister from a very limited list.

Each party was required to name three candidates before the last election, and Pheu Thai has now used up two, after the court’s dismissal of Srettha Thavisin last year.

Their third candidate, Chaikasem Nitisiri, is a former minister and party stalwart, but has little public profile and is in poor health. The alternative would be Anutin Charnvirakul, the former interior minister whose Bhumjaithai party walked out of the ruling coalition, ostensibly over the leaked phone call.

Relations between the two parties are now strained, and Anutin would have to rely on Pheu Thai, which has many more seats, to form a government, which is hardly a recipe for stability.

The largest party in parliament, the 143 MPs who were formerly in the now-dissolved Move Forward and have reformed as The People’s Party, has vowed not to join any coalition, but to remain in opposition until a new election is held.

A new election would appear to be the obvious way out of the current political mess, but Pheu Thai does not want that. After two years in office it has been unable to meet its promises to revive the economy.

For all of her youth, the inexperienced Paetongtarn failed to establish any real authority over the country, with most Thais presuming that her father was making all the big decisions.

But Thaksin Shinawatra seems to have lost his magic touch. Pheu Thai party’s signature policy at the last election, a digital wallet which would put B10,000 ($308; £178) in the pocket of every Thai adult, has stalled, and been widely criticised as ineffective.

Other grand plans, to legalise casinos, and to build a “land-bridge” linking the Indian and Pacific Oceans, have gone nowhere.

At a time when Thai nationalist sentiment has been fired up over the border war with Cambodia, the Shinawatra family’s long-standing – though now broken – friendship with Hun Sen has heightened suspicion in conservative circles that they will always put their business interests before those of the nation.

The party’s popularity has plunged, and it is likely it would lose many of its 140 seats in an election now.

For more than two decades it was an unbeatable electoral force which dominated Thai politics.

It is hard to see how it will ever regain that dominance.