On reports that the BJP is likely to attend the JPC meeting on Thursday, ending its boycott of the panel to once again press for inclusion of Singh and finance minister P Chidambaram as witnesses, he said it was "most welcome".
The BJP members reported decision to attend the JPC meeting has proved that there was no justification for their boycott, he said.
On summoning Chidambaram as witness, Chacko said it would be "decided on the basis of consensus".
Referring to the allegation of CPI leader Gurudas Dasgupta that the Attorney General was not called before the JPC on October 11, Chacko said he was out of the country that day.
Attorney General GE Vahanvati would be appearing before the JPC, he added.
He said the extended period of the JPC would expire by December and one more extension would be essential as only 75% work was completed.
The mobile operators association had been called for tomorrow's JPC meeting, Chacko said.