(By Denis Greenan). Rome, December 5 - Italy is looking to replace its widely criticised Porcellum or 'pig-sty' election law after the Constitutional Court struck it down Wednesday. The court, in a long-awaited ruling, said the law was unconstitutional because of two things. First, it said a mechanism granting a huge bonus to the winner in the House was against the fairness doctrine enshrined in Italy's postwar founding document. Second, and for the same reasons, it ruled against a system that prevents voters from picking their representatives in constituencies. Since the law was introduced in 2006, party leaders have put hand-picked candidates on so-called 'blocked lists' which were then voted on, with the top names entering parliament according to the percentage of the vote won. Premier Enrico Letta, of the centre-left Democratic Party (PD), has said changing the electoral law will be one of the first items for his new, smaller but more cohesive government with the New Centre Right (NCD), a splinter group from Silvio Berlusconi's recently disbanded People of Freedom (PdL) party. The NCD broke away when it refused to sink Letta after the PD insisted on applying an anti-corruption law to oust Berlusconi from the Senate on a tax-fraud conviction last month. Berlusconi's revived Forza Italia (FI) party went into opposition. The PD-NCD alliance faces a key confidence vote in the December 11 on a revamped reform agenda. While it has a large majority in the House, thanks to the bonus, its majority in the Senate has now been cut to about a dozen on paper because of FI's exit. On Thursday officials rejected claims from FI and the biggest opposition group, former comedian Beppe Grillo's anti-establishment 5-Star Movement (M5S), that parliament had lost its legitimacy because of the Constitutional Court's ruling. "Parliament is fully legitimate, the Court itself does not call that into doubt," said Italian President Giorgio Napolitano. He stressed that, in its ruling, the court said it was up to parliament to frame a new law. Replacing the Porcellum, he said, was "imperative". The main problem was whether there was "the political will" to do so, the head of State said. House Speaker Laura Boldrini also rejected claims from the opposition that parliament had been delegitimized by the ruling. "This House is fully legitimate and legitimized to function," she said, responding to heckling from the M5S. Parties also began arguing over where an electoral-reform bill should start its parliamentary journey. In response, Boldrini said she would talk to Senate Speaker Piero Grasso to decide where the bill should be presented. The Porcellum, passed under a previous Berlusconi government, has been widely blamed for leading to inconclusive February election results, months of political deadlock, and Letta's unprecedented left-right coalition government with traditional foe the PdL. The PD and PdL were engaged in constant sniping that hampered lawmaking. The PD and NCD are closer on many points. The Porcellum's architect, Northern League heavyweight Roberto Calderoli, admitted a day after it was passed that it was a 'porcata' or "mess", leading to the pig-Latin tag it was given. The Porcellum militated against any party getting a solid majority in the Senate, which has equal lawmaking status with the House. Calderoli has since frankly admitted it was specifically designed to stop the centre left, which had a big advantage in the 2006 pre-election polls, from achieving a stable majority in both houses. In the end Romano Prodi squeaked home by only two seats in the Upper House and struggled to keep a weak and fractious coalition together for two years. Current reform plans all envisage stripping the Senate of lawmaking powers. Two PD Senators filed a bill Thursday to scrap the Senate altogether. Parties are divided, however, on whether to turn to German-style proportional representation (PR), a French system with two rounds of voting, or a mostly first-past-the-post system. Napolitano on Thursday urged the parties not to reconsider PR, which he said had been scrapped 20 years ago. Efforts to change the Porcellum have foundered on several occasions in the last few years.