ROME (Reuters) - The Italian government won all five confidence votes it had called in the upper house of parliament on Wednesday on a new electoral law that looks unlikely to produce a clear-cut result at national elections due by next May. Prime Minister Paolo Gentiloni called the five confidence motions to get the package approved quickly despite furious opposition from the anti-system 5-Star Movement and small leftist groups. All five of the motions, on different articles of the law, garnered comfortable majorities, even though many leftist allies had deserted coalition ranks. The bill has already passed through the lower house. A sixth vote on another article, but which was not the subject of a confidence motion, also passed. A final vote on the law is scheduled for Thursday morning. The proposed voting system favors parties that form pre-election coalitions and is backed by the largest parties within Italy s main centre-left and centre-right blocs. It will penalize groups that want to go it alone, such as 5-Star. However, opinion polls indicate that the system, which is a mix of proportional representation and first-past-the-post, will not throw up an obvious winner, with the vote split three ways between the left, right and 5-Star. A YouTrend survey for AGI newsagency said on Wednesday that none of the three main groups would get  anywhere near an absolute majority of seats .  It said the only way for this to happen would be for one bloc to win more than 40 percent of the vote, adding this would trigger a landslide. At present, none of the three political groups are seen winning support of more than 33 percent.   Five-Star has denounced the reform as  an institutional coup d etat  and senators from the group closed their eyes, or put on a blindfold as they voted  no  in the Senate. Hundreds of their supporters filled a central Rome square to denounce the bill, chanting  honesty  and waving party flags.  This is a fraudulent law for people here. It ignores voting rights and instead favors amalgamations and hookups,  said Rossano Cioccolini, 56, a worker from the northern city of Milan who took a day of holiday to join the Rome rally.  The largest party in Italy, 5-Star, will not get a look in because it doesn t accept alliances,  he added. The use of multiple confidence motions first in the lower house and now in the Senate has allowed the ruling centre-left coalition to truncate discussion on the bill and sidestep dozens of secret votes that could have allowed disillusioned lawmakers to betray their camp and ambush the bill. The government says the new law is needed to harmonize the electoral system for the upper and lower houses and reduce the risk of different majorities materializing in the two chambers. Previous attempts at reform this past year have all failed. Critics say the proposed law will enable political leaders to pack electoral lists across the country with their most avid supporters, stifling internal party debate. 