By Caroline Wyatt BBC Paris correspondent

He was found guilty of allowing party employees from Mr Chirac's former RPR party to be put on the payroll of Paris City Hall, when Mr Chirac was mayor and Juppe its finance director.

Juppe's party and leader are backing him despite verdict

The verdict raised fresh questions in France over Mr Chirac's own conduct as mayor.

The president has also launched an official inquiry into allegations that the judges examining the Juppe case were threatened and their offices were broken into in the run-up to the verdict.

On French TV and radio, Mr Chirac has dominated the headlines with his own personal reaction to the criminal conviction of his closest ally.

Long Mr Chirac's heir-apparent as president, Juppe is still the head of his new UMP political party too.

Yet all was thrown into doubt when he was found guilty of helping illicitly fund the RPR in the early 1990s.

As finance director to Mr Chirac's Paris mayor, he put seven party employees on the municipal payroll.

I hold him in the highest esteem and respect him. He is a politician of exceptional quality, with immense ability, humanity... honesty President Jacques Chirac

Juppe was given an 18-month suspended prison sentence, which should automatically bar him from political office for the next decade.

Yet Mr Chirac leapt to his defence, encouraging him to lodge an appeal against the sentence, to keep Juppe at his side.

"Alain Juppe is a friend," he said.

"I hold him in the highest esteem and respect him. He is a politician of exceptional quality, with immense ability, humanity... honesty. And France needs men of such quality."

The cameras were there too, as Juppe arrived at work at his other job as mayor of Bordeaux. But he was reluctant to speak to waiting reporters, except to promise them fresh comment later.

Juppe is expected to make a statement on Tuesday on whether or not he plans to stay on in politics.

The facts date back to 10 years ago to a time when there was no official system to fund the parties and all parties used such means to finance themselves Natalie Kosciusko-Morizet UMP MP

MPs from his own party, the governing UMP, such as Natalie Kosciusko-Morizet, believe he must stay in office.

"The judgement of Alain Juppe is felt as very tough, very heavy by all politicians and also the population - nobody has ever suspected his personal probity, and the facts date back to 10 years ago to a time when there was no official system to fund the parties and all parties used such means to finance themselves," she said.

She is horrified by suggestions in the French and foreign media that perhaps Mr Chirac's own conduct while mayor of Paris should also be put under the spotlight again.

An investigation into his own knowledge of the party funding scandal had to be halted after he claimed presidential immunity, as did a separate investigation into his expenses while mayor of Paris.

Yet Ms Kosciusko-Morizet says no-one should use Juppe's conviction as a weapon against the president.

'Disgusted'

"I am personally disgusted by a certain campaign arranged by people to call for the dishonesty of Jacques Chirac - he is in the situation where he has immunity, because he is the president and can't defend himself, and accusing somebody who can't defend himself is I feel disgusting," she said.

Legal experts say little or nothing can be done to investigate Mr Chirac while he remains in office, even if some prosecutors would like to.

It remains to be seen what can be found against the president and to what extent it can reach him Florence Faucher Paris Centre for the Study of Political Science

However, Florence Faucher of the Paris Centre for the Study of Political Science says Juppe's conviction may cause some to ask questions.

"The decision on Juppe is particularly close to Mr Chirac, because Juppe is such a close ally of the president and because the affair is linked to the mayor of Paris, a position Mr Chirac held from 1976 to 1995," she said.

"It's getting closer to the president, However, it remains to be seen what can be found against the president and to what extent it can reach him."

Public reaction

Yet on the streets of Paris, there's little interest in finding out how much Mr Chirac knew about the illicit funding of his own party.

Perhaps these kind of people like Mr Chirac have lots of responsibilities and they don't do this for money, so I think they don't have to face justice for every kind of subject French passer-by

"He may have been corrupt in the past and maybe he still is, but it must be taken into account what he does as president," one person told me.

Another passer-by said: "Perhaps these kind of people like Mr Chirac have lots of responsibilities and they don't do this for money, so I think they don't have to face justice for every kind of subject."

What many are wondering, though, is who tapped the phones of the judges in the Juppe case, and may even have tried to break into their offices?

Mr Chirac has launched an inquiry, and conspiracy theories abound.

Chirac wants his protege Juppe to succeed him as president

So what impact, if any, will this latest of so many scandals have on the French president?

"As a president in office he has immunity from any indictment or sentencing but once he's not in the Elysee Palace any more, God knows what might happen," said Charles Lambroschini of the centre-right newspaper, Le Figaro.

Mr Chirac can stay in power for another three years - but without Juppe at his side to control his party, he could be very vulnerable to other challengers for his crown, not least the ambitious interior minister Nicolas Sarkozy.