The trial of former French president Nicolas Sarkozy on charges that his unsuccessful 2012 re-election bid was illegally financed has formally started.

Sarkozy, 66, is facing allegations that he spent almost twice the maximum legal amount of 22.5 million euro (£19.41 million) on the presidential race he lost to Socialist Francois Hollande. He has denied wrongdoing.

Sarkozy was not present at the Paris court, where he was represented by his lawyers. The trial is scheduled to last until June 22.

Sarkozy, who was president from 2007 to 2012, faces up to one year in prison and a fine of 3,750 euro (£3,235), if found guilty.

The proceedings got under way less than three months after Sarkozy was convicted of corruption and influence peddling in another case. He has appealed against that verdict.

Following several scandals, French law since 1990 has strictly limited political campaign spending.

According to the judicial investigation in his case, Sarkozy “indisputably benefited from fraud that allowed him to have, during his 2012 campaign, resources much superior to what the law authorised”.

An investigative magistrate concluded that Sarkozy and his close entourage decided to hold “spectacular and expensive rallies”. The campaign’s total cost allegedly reached at least 42.8 million euro (£36.9 million).

The investigation did not establish whether Sarkozy allegedly participated in trying to cover up the overspending, which included forging invoices, or ordered fraudulent actions himself.

In addition to the former president, 12 other people and the company in charge of organising the campaign rallies are facing trial on charges that include forgery, breach of trust, fraud and complicity in illegal campaign financing.

During the judicial investigation, some of them admitted wrongdoing.

Former deputy campaign director Jerome Lavrilleux described on national television in 2014 a system of fake invoices that allegedly allowed the conservative party, then named UMP, to pay for the campaign rallies, with the alleged complicity of public relation firm Bygmalion.

The scandal prompted a destructive battle within the party as its leaders blamed each other.

Sarkozy has denied that illegal money financed his campaign. Speaking to investigative magistrates, he asked: “Where is the money?” suggesting that some people within his party might have misused it.

He also said he does not remember two notes from his campaign accountants, allegedly given to him weeks before the election, warning against racking up additional expenses.

The UMP party was renamed The Republicans in 2015. One year later, Sarkozy ran for president again and was defeated in the conservative primary.

Sarkozy retired from active politics in 2017 but still has a lot of influence within The Republicans. French media have reported that he maintains regular contact with President Emmanuel Macron, whose first term ends next year and whom Sarkozy is said to be advising.