(ANSA) - Rome, September 20 - The Senate has launched an inquiry after Thursday's session of the Upper House was briefly suspended because there was no duty speaker to oversee proceedings. Experts said it was the first time such an incident has taken place in the history of the Italian Republic. The Senate Speaker is Renato Schifani of former premier Silvio Berlusconi's People of Freedom (PdL) party, but he has four deputies who also oversee sessions of the Upper House. The situation was caused because the duty speaker, Domenico Nania of the PdL, was delayed and unable to take over when Emma Bonino of the Radical party finished her shift in charge. Another deputy speaker, Rosi Mauro of the Northern League, stepped in but she had to leave to catch a flight, so the session had to be suspended during debate about a motion on violence against women until the arrival of Schifani. Anna Finocchiaro, the Senate whip for the centre-left Democratic Party, expressed indignation. "What happened today is totally unacceptable," she said. "Abandoning the floor (of the assembly) would be extremely serious in the council of a town of just a few people, never mind the Senate of the Republic". Schifani did not try to downplay the gravity of what happened. "I will acquire all the data necessary to have correct information about what happened but I want to say in any case that one thing is certain," he said, "the interruption of the work of a parliamentary chamber because of the absence of the person who should oversee it is a regrettable incident. "I will carry out an inquiry and then I'll report to the floor (of the Senate) and the (party) whips".