About two dozen people, including policemen and mediapersons, were injured today when police lobbed tear-gas shells and resorted to lathicharge on the Samajwadi Party rally which turned violent. Police also lobbed stones at the crowd and later opened blank fires.SP youth wing members, defying ban orders of the Mayawati government, were demonstrating outside their party office where they had been gathering since last evening. The unruly crowd threw stones at PAC and RAF jawans as well as the police. They damaged a few police vehicles and also burnt a police jeep, a motor-cycle and a cycle.Policemen too damaged many vehicles of party leaders parked outside the office. Some tear-gas shells hit party workers who were being addressed by party president Mulayam Singh, general secretary Amar Singh, Shivpal Singh Yadav and Mulayam Singh’s son MP Akhilesh Singh inside the party office complex.Normalcy returned when on Mulayam’s directive about 2,000 party workers, led by Shivpal and Akhilesh, courted arrest. Later, Mulayam said they were only staging a peaceful demonstration. He alleged policemen in plain clothes had triggered the violence and burnt vehicles.However, denying that police opened fire, Principal Secretary (Home) said about 8,000 preventive arrests had been made. The arrested include four MPs, one MLC and 21 MLAs. He claimed that police resorted to lathicharge after provocation from the SP workers.Meanwhile Mulayam, describing the police attack on his party workers as an attempt to repress the right of Freedom of Expression granted in the Constitution, said if opposing misrule of a government and misuse of POTA was a crime his party would commit it again and again.Claiming the success of the demonstration, he alleged that the Mayawati government wanted to eliminate the party leadership. ‘‘The police attack on us inside the office is an indication of this,’’ he said.About his party’s future course of action, he added that a national party convention would be called soon to take a decision. The date would be finalised at a meeting of party leaders on February 25, he said.Demanding the arrest of Mayawati and Lalji Tandon under POTA, Amar Singh said his party workers were attacked by police at the behest of PM A.B. Vajpayee and L.K. Advani. It was Tandon’s ‘‘blue-eyed boy’’ DM Navneet Sahgal who ordered police firing and lathicharge.On the allegation that he was playing Thakur politics, the SP leader said: ‘‘No eyebrows are raised when Mayawati plays Dalit politics.’’Meanwhile, the injured, including driver of Mulayam Singh’s son Akhilesh Singh, are undergoing treatment in the local Shyama Prasad Mukherjee Civil Hospital. SP leaders have demanded an inquiry into the incident by an Assembly or Parliamentary committee. ‘‘Only then the truth will come out,’’ party leader Janeshwar Mishra said.