Leading historians have rubbished the Spanish supreme court’s claim that General Franco was head of state from October 1936, almost three years before his rebellion secured victory in the Spanish civil war.

The claim was made in the court’s latest ruling on the socialist government’s tortuous efforts to exhume the dictator’s remains from his hulking mausoleum and have him reburied in the family vault.

In the course of explaining why it had decided to suspend next week’s planned exhumation to give Franco’s family more time to appeal against the decision, the court referred to him as “head of state from 1 October 1936 until his death in November 1975”.

The assertion was met with derision by experts on the period. The British Hispanist Paul Preston, who wrote a biography of Franco, described it as “bollocks”.

He said: “The only way these people at the supreme court could think this is right, that Franco was head of state from that time, would be if they thought that the military coup of 1936 was totally legitimate.”

Preston pointed out that the rebel generals had met in late September 1936 to agree on who should be their overall military commander, or generalísimo.

“There’s a coup and within that coup a certain kind of competition between generals – a bit like the succession to Theresa May – to see who gets to be top dog,” he said.

A week later, they reluctantly agreed a decree to confirm Franco as head of the Spanish state’s government for the duration of the war, working on the assumption that the monarchy would eventually be restored.

Franco’s claim to be head of state had no legal basis, Preston said.

Julián Casanova, who teaches contemporary history at the University of Zaragoza, said the head of state at the time was clearly Manuel Azaña, the president of the republic.

“Franco was named head of the government of the Spanish state by his coup-waging colleagues and that title only existed in the areas they’d conquered,” he told the online newspaper eldiario.es. “Manuel Azaña was [the head of state] and continued as such until the victory of Franco’s troops on 1 April 1939.”

The supreme court did not respond to a request for comment, but Preston saw the judges’ error more as proof of Franco’s enduring legacy than “any kind of deliberate, machiavellian plan”.

“I can’t tell you what went on in their minds,” he said. “What I can say is that this reflects what we call sociological Francoism … Generations of people were brought up in the Franco regime with everything that that meant: the education system, the media. They were subjected to the brainwashing that the entire nation was subjected to during the Franco regime.”

Casanova said a body of good historical writing had been available for years, but that Spaniards were still not learning enough about their country’s recent past. “Spain’s 20th century history, rigorously researched, based on solid sources and filtered by historiographical debates, has taken its time in reaching classroom and universities,” he said.