The already shaky ruling Centre Left coalition of Romano Prodi suffered a potentially damaging blow this morning when Clemente Mastella, the Justice Minister, resigned following the arrest of his wife on corruption charges.

"I am throwing in the towel," Mr Mastella said in a speech to Parliament. He attacked the warrant for the house arrest of his wife, Sandra Lonardo, who chairs the council of the Campania region, as "the latest in series of attempts to discredit me".

Mr Mastella represents a small Christian Democratic faction which forms part of the Centre Left coalition. Mr Prodi, elected eighteen months ago, has a comfortable majority in the Lower House but a wafer thin majority in the Senate. It is not clear whether Mr Mastella's party will withdraw from the coalition following his resignation.

Sandra Lonardo - who like many married Italian women uses her maiden surname professionally - complained that she had learnt of the arrest order from television news bulletins before she had been officially notified. The charges relate to alleged "abuse of public office".

Prosecutors in the Naples suburb of Santa Maria Capua Vetere allege that the minister's wife used her position in the Campania region to "influence" the award of public contracts and in particular to "trade favours" with the director of a state hospital in Caserta. She denied the charges, saying, "I feel absolutely serene, I have nothing to fear and I will provide the judicial authorities with whatever clarification they request from me."

She added: "I believe this is the bitter price, that together with my husband, we are paying for our defence of Catholic values in politics, for the principles of moderation and tolerance against all fanaticism and extremisms".

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