Imran Khan faces the greatest challenge of his political career after Pakistan’s supreme court ruled that the prime minister’s attempt to avoid a no-confidence vote by dissolving parliament was unconstitutional.

The ruling, announced late on Thursday evening, set the stage for a weekend showdown in the national assembly that is widely expected to end the charismatic former cricket captain’s four-year premiership.

The court decision capped a tumultuous few days for Khan and his country. To justify dissolving parliament and calling new elections, Khan had accused rivals of conspiring in a US-led plot to remove him over his support for Russia. Washington and opposition leaders strongly denied the allegation.

Analysts said that the constitutional crisis triggered by Khan’s move to dissolve the parliament risked undermining Pakistan’s fragile democratic institutions.

Shahbaz Sharif, leader of the opposition Pakistan Muslim League-Nawaz and a potential candidate to succeed Khan if the prime minister loses a no-confidence vote set for Saturday, said the court judgment marked an “epoch-making day”.

“Today, politics of lies, deceit and allegations has been buried,” Sharif wrote on Twitter.

But analysts added that instability in the nuclear-armed country of 220mn would persist.

Even some of Khan’s harshest critics had been shocked by his tactics in response to losing his parliamentary majority last week due to the defection of the main coalition partner of his Pakistan Tehreek-e-Insaf party.

In an address to the nation this week, Khan invoked two 18th-century Indian courtiers infamous for betraying Indian rulers to British imperialists — Mir Jafar and Mir Sadiq.

“Today, we have Mir Jafars and Mir Sadiqs here,” Khan said, calling on loyal Pakistanis to “step forward and stop this conspiracy”.

Khan’s rhetoric underscored Pakistan’s rift with the west and drift towards Russia and China in recent years. But he offered no proof for his conspiracy claims other than a letter he brandished on television. Officials later revealed it was a cable from Pakistan’s ambassador in Washington.

Moscow has backed Khan’s assertions that the US interfered in Pakistan’s internal affairs “to punish the ‘disobedient’” prime minister. Washington denies seeking regime change and said it supported Pakistan’s constitutional process.

Critics said Khan’s allegations of treachery revealed a darker side to the populist leader, whose image is still burnished by past sports stardom. A 2021 YouGov ranking of the world’s most admired men put Khan in 17th place, just behind the Pope.

“People in the Commonwealth [of Nations] have focused on him as this cricketer celebrity,” said Husain Haqqani, senior fellow at the US Hudson Institute and a former Pakistani ambassador to Washington. Even as Khan espoused conservative religious views and sympathy for Afghanistan’s Taliban, he escaped being “scrutinised as a normal politician”, said Haqqani, who denied Khan’s allegations of being part of the plot against the prime minister.

Known as a playboy in Britain’s 1970s and ’80s high society, Khan the cricketer had a pristine record for fair play, despite encountering “ingrained racism at almost every level”, said his biographer, Christopher Sandford.

But Sandford added that the tenacious captain “did have a habit of seeing any slight or setback as being part of almost a conspiracy”. In one episode, he recalled, Khan “became obsessed that [an English umpire] was intrinsically anti-Pakistan”.

Khan won the 2018 general election promising to fight corruption and build a “New Pakistan” with a strong welfare system. But his parliamentary majority was slim and analysts said his grip on power had been weakened by the loss of support from Pakistan’s powerful military.

Khan’s ousting would have implications for Pakistan’s fraught relationship with Washington. He has been a vocal critic of what he calls US over-reach in its “war on terror”. Yet Pakistani officials have also griped that President Joe Biden has not arranged a call with the prime minister.

Vladimir Putin has been more welcoming, and Khan was happy to proceed with a visit to Moscow on the day Russia invaded Ukraine. “What a time to come. So much excitement,” he remarked on the airport red carpet.

While Khan lashes out at perceived western foes, his more pressing problems are his fracturing political support, a galvanised opposition and a cost-of-living crisis.

Food prices were 17 per cent higher year on year last month, according to Pakistan’s Bureau of Statistics. About 64 per cent of respondents to a Gallup Pakistan poll considered inflation the country’s biggest problem.

On Thursday, Pakistan’s central bank raised its policy interest rate 2.5 percentage points to 12.25 per cent to try to stem falls in the value of the rupee.

Khan’s PTI party hopes the spectre of foreign interference will rally supporters. Omar Ayub Khan, a senior PTI politician, said the prime minister was enjoying a “groundswell” of approval.

“Our government has upheld the dignity and self-respect of the country, as US interference in Pakistan’s affairs has worked in our favour,” he said. “Our people will eat grass [to survive] if you give them self-respect.”

But many voters were unmoved by talk of foreign plotting. “I am struggling to meet my household expenses,” said Saeed Hussain, a car washer in Islamabad. “My income has gone down. This is my immediate concern, not some conspiracy.”

Still, Khan made clear after the supreme court ruling that he was far from conceding political defeat, saying he would address the nation again on Friday evening.

He added a cricketing metaphor to express his resolve: “My message to our nation is I have always and will continue to fight for Pak till the last ball,” he wrote on Twitter.