Former French president Nicolas Sarkozy lost his fight yesterday against a decision by election auditors that found his conservative UMP party went over budget during his 2012 election campaign.

The Constitutional Council’s ruling against him plunges the opposition UMP into financial crisis as it was ordered to return the 11mn euros ($14mn) of state money it had been advanced, as a penalty for running over budget.

It is the latest blow to the party after a tumultuous year which saw it torn in two in an acrimonious leadership struggle in the wake of Sarkozy’s defeat to Socialist Francois Hollande in May 2012.

It also creates another headache for Sarkozy, who has dropped heavy hints that he is mulling a comeback for the 2017 election but has been entangled in a series of legal cases.

In a swift protest at the ruling, Sarkozy said he was quitting his post as a member of the Constitutional Council, a body which rules on constitutional issues, including election disputes and automatically bestows membership to ex-presidents.

In France, election funding is capped, large donations are banned and the state subsidises campaign spending.

The council, which counted 12 members including Sarkozy, upheld a December 2012 decision by the national campaign financing watchdog that Sarkozy’s campaign spending during his run-off against Hollande went over an allotted budget of 22.5mn euros.

Whereas the watchdog calculated the overspending at 300,000 euros ($389,000), the court said that Sarkozy overspent by 466,118 euros, or 2.1% above the ceiling.

In a statement to AFP, Sarkozy said this was to “regain his freedom of speech” to react to the decision.

It is the first time that a candidate reaching the second round of presidential elections has seen his campaign expenses rejected.

Sarkozy has been implicated in a series of campaign funding scandals allegedly involving Liliane Bettencourt, France’s richest woman, and former Libyan dictator Muammar Kadhafi. But he has consistently denied any wrongdoing.

The UMP is already in financial trouble as its funding has been affected by the fall in the number of its lawmakers. French parties receive grants from the government based on their strength in parliament.

UMP leader Jean-Francois Cope called for a “massive national contribution” in the wake of Sarkozy’s resignation, saying it was necessary to “prevent the French political arena from being monopolised by the left and radical parties”.

Cope, who held an emergency meeting with Sarkozy late on Thursday, said the Council’s ruling would seriously affect the “means available to the main opposition party to serve French democracy”.

The decision also comes just days after UMP activists voted to maintain Cope as the party head until 2015 and the organisation of primary elections a year later to pick its presidential candidate.