By Peter Allen, Paris

The possibility was raised by judicial sources before the former French president’s visit to the Palais de Justice in Bordeaux.

There he will be questioned at length by Judge Jean-Michel Gentil over his links with Liliane Bettencourt, the l’Oreal heiress and France’s richest woman.

The principal allegation in the so-called ‘Bettencourt Affair’ is that Mr Sarkozy accepted thousands of pounds in illegal cash to fund his election campaign in 2007.

In return, it is claimed, Mrs Bettencourt was offered massive tax breaks on her multi-million pounds fortune after Sarkozy came to power.

While some believe Mr Sarkozy will be quizzed “as a witness”, judicial sources told AFP, France’s national news agency, that “he may be indicted”.

This would mean him facing the kind of criminal trial which his former mentor and predecessor as conservative president, Jacques Chirac, went through.

Mr Chirac ended up receiving a suspended prison sentence for fraud last December, becoming the first head of state in the history of the Fifth Republic to be treated as a common criminal.

Judge Gentil is examining evidence that Mr Sarkozy “abused the weakness” of Mrs Bettencourt, 90.

Investigators are examining the withdrawal of hundreds of thousands of euros from Swiss bank accounts, and the claim that cash was delivered in brown envelopes.

Mr Sarkozy, who lost May’s presidential election to Socialist Francois Hollande, has denied a series of allegations of illegal campaign financing.

Police raided the Paris mansion Mr Sarkozy shares with his third wife, Carla Bruni, in July – just weeks after he lost his presidential immunity from prosecution.

Mr Sarkozy’s legal troubles mounted on Tuesday when it emerged that judges are investigating millions he spent on opinion polls when he was president.

The allegation is that he enriched friends who produced the polls, many of which were used for personal reasons including gauging how popular Carla Bruni-Sarkozy was as First Lady.

Mr Sarkozy is also being investigated over the Karachi Affair – a fraud inquiry centred on submarine sales to Pakistan – and allegations that he received millions from former Libyan despot Muammar Gaddafi.

Despite all this, Mr Sarkozy, who is attempt to carve himself a new career as an international speaker in the Tony Blair mould, has not ruled out running for president again in 2017.

Mr Sarkozy’s aides said he was delivering a speech in London today.

Separately reports emerged that the US ‘spied’ on Mr Sarkozy”s presidency by hacking into ministerial computers during his last weeks in office, it was claimed yesterday.

France’s cyber-warfare agency believes that a computer virus found in the Elysee was similar to Flame, which was allegedly created by a US-Israeli team to target Iranian computers.

It is thought to have been used on computers of Sarkozy aides including Xavier Musca, his chief of staff during the presidential election.

Janet Napolitano, US Secretary of Homeland Security, did not deny the Elysee Palace hacking allegations, but said: “We have no greater partner than France, we have no greater ally than France.”