His remark comes as Sinhala nationalists accuse the government of trying to bring in a new constitution secretly, according to radiogagana.com.
He was speaking at a public seminar on a Constitutional Council subcomittee report in Jaffna on February 11 organized by the Bar Association of Sri Lanka.
Sumanthiran said a new constitution adopted by parliament should be passed at a referendum, or else it would suffer the same fate that of the 13th amendment.
Politicians of the south have a responsibility to explain to the Sinhala voters the need for a new constitution, he said and extended his support to eliminate any fears among them.
Asked by dean of the Jaffna University’s law faculty Kumaravadiwel Gurubaran what the TNA would do if its proposal failed, the MP said the next step could be decided only by acting without allowing anyone to question the honesty and commitment of the Tamil people.
BASL president Geoffrey Alagaratnam presided at the seminar, where Dr. Kalana Senaratne of the Peradeniya University’s law faculty also spoke.