Reacting to the court's decision, an elated Singh said he was "thrilled" and felt vindicated, but was dismayed that a court had to intervene in the matter.
"It is a matter of satisfaction that the court has lifted the ban on the book (Jinnah: India, Partition, Independence)," Singh said, adding the court had upheld freedom of speech.
The three-member bench headed by Chief Justice K S Radhakrishnan said in its order said, "It (the ban) amounts to making a serious inroad into the fundamental rights guaranteed under the Constitution of India."
The Gujarat government had issued a notification on August 19 banning Singh's book on the grounds that it was against "national interest" and the contents were "misleading".
In some hard-hitting observations, the court said, "It is difficult to believe that the author of the notification has really read or comprehended what the author of the book has to say."
The notification was silent as to how the contents of the book would "affect and disturb" public tranquility or interest of the state, the judges said.
"No opinion has been expressed by the state as to how public tranquility would be disturbed. Lack of opinion means lack of thinking. Lack of thinking means lack of understanding," the court said.
The court observed that the notification issued by the state government under Section 95 of the Code of Criminal Procedure fell short of statutory requirements of that section and hence "could not stand in the eyes of law".
Asked whether the ban will be imposed again, Gujarat government spokesman Jayanarayan Vyas said, "We should await the judgment, then a mature decision will be taken."
Singh said the ban on his book by the Modi government in Gujarat was "supported" by the Congress and termed it was "doubly a matter of concern".
When asked whether the ban on the book was politically motivated, he refused to comment but added that the Gujarat government should think about the court's observation that it had banned the book in haste.
Singh said the ban on his book had "derailed" things "which have now again come on track... my book was banned and its copies burnt".
The Darjeeling MP said he could not help if the BJP saw all the "demerits in me" after his expulsion when asked why he was "disclosing" issues that go against the interest of the party at this stage.
Singh, a former external affairs and finance minister, said he was planning to write a political biography on the life of the country's last Governor General C R Rajagopalachari.
"Over the years, I have gathered material in the form of political diaries. I am thinking what to do with it," he said.
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