New Delhi, Dec. 11 -- The Opposition's main agenda is to keep undocumented migrants in the voter list but the government will fulfil its constitutional duty to "detect, delete and deport" them, Union home minister Amit Shah said on Wednesday, adding that the Congress lost elections not because of vote theft but poor leadership. In the Lok Sabha, a combative Shah said the Opposition was spreading one-sided lies about the special intensive revision for the last four months in an attempt to mislead the people, and asked why the Opposition was contesting elections if it believed the voter rolls were manipulated. The speech also saw a brief face-off between an angry home minister and leader of the opposition in the Lok Sabha Rahul Gandhi, and a walkout by the Opposition later. Prime Minister Narendra Modi lauded Shah's speech, saying he exposed the Opposition's lies about the election process. Replying to the debate on electoral reforms, Shah launched a frontal attack on the Opposition and said, "Their main agenda is to keep illegal immigrants in the voter list." As many Opposition parties walked out, the minister added, "Even if they walk out 200 times, we will not allow even one illegal immigrant in the country. Our policy is to detect, delete (from electoral lists) and deport. We will complete the constitutional duty." "Their (Opposition's) policy is to normalise intruders, and add names in the electoral roll to formalise them. It is my party's policy and I also believe that such a major demographic change is a danger to the country. This country has been divided on the basis of population in the past. We don't want our future generation to face another partition," the home minister added. "SIR is a constitutional process, and by questioning it, the Opposition is tarnishing India's democratic image globally." The minister also linked illegal intrusion with the safety of democracy in India. "Can a country's democracy remain safe if illegal migrants decide who would be the PM and the CM? This SIR is nothing else but cleaning up of the voter list. I can understand some parties have political problems due to SIR. I feel sorry for them. Indians did not vote for them. Those foreigners who voted, now they will be deleted from the list. We have to decide whether foreigners will have voting rights to form Parliament and state assemblies. My opinion is, this cannot happen," Shah said. The home minister informed the House that out of the 2,216km of the Indo-Bangladesh border in Bengal,1,653km was fenced. "The remaining 563 kms are open in only Bengal. We have completed border fencing in Assam, Tripura, Meghalaya, J&K, Punjab. Rajasthan and Gujarat. Only the Bengal border has been kept open," he said. With elections in West Bengal due next year, Shah slammed the Trinamool Congress-led state government and cautioned the latter that if it protected illegal migrants, it will also be voted out. "Don't you have any responsibility? When the illegal migrants enter India, their ration card, Aadhaar card, enrolment in voter lists are made in villages. They are playing with national security. You may win an election with the support of these migrants, but you compromise on national security. I want to say today, Bihar people have made a big decision against 'ghuspetiyan bachao' rally. Bengal is also going to do the same," Shah said, possibly referring to Rahul Gandhi's Voter Adhikar Yatra in Bihar earlier this year. Shah alleged that there were three instances of vote theft - by Jawaharlal Nehru, Indira Gandhi and Sonia Gandhi. "After Independence, Sardar Vallabhbhai Patel was backed by 28 persons, while Jawaharlal Nehru was supported by two persons and yet Nehru became the prime minister, this was vote chori," he said. Shah said the second "vote chori" was by Indira Gandhi, when she granted herself immunity after the court set aside her election, referring to the Allahabad high court countermanding her 1971 win from Rae Bareli. He said the dispute of the third vote theft just reached the courts on how Sonia Gandhi "became a voter before becoming a citizen of India", which drew protests from the Congress over the fact that the courts had dismissed a similar case. Shah also said the reason for the Congress's poll losses was its leadership. "If someone asks a question in a presser, he is dubbed as a BJP agent, if they lose a case, they accuse the judge, if they lose an election, they blame EVMs. Now, when the EVM blame does not hold, they brought up vote theft... still, they lost Bihar. Now the reason for your defeat is your leadership and not EVM or voters' list," the home minister said. "They think no one holds them accountable.I hope I am proved wrong and one day Congress workers seek accountability," he said. Interrupting his speech, Rahul Gandhi challenged the home minister to debate with him on his three press conferences in which the Congress leader had alleged vote theft by the BJP in collusion with the Election Commission. "Let us have a debate on my press conference. Amit Shah ji, I challenge you to have a debate on the three press conferences," the Congress leader said. Shah shot back and said he will not frame his speech according to the wishes of the Leader of Opposition and also not change the sequence of his argument on someone else's demand. In his reply, Shah pointed out that for 73 years, the PM alone decided the chief election commissioner and the election commissioner and explained the question of immunity to the election commissioners. "It is the Modi government that included the Leader of the Opposition in the committee....