"Old days are back," Vajpayee quipped as he came out of Parliament after taking oath as a member in the Lok Sabha.

Asked about the role of his party, he told reporters its members would not indulge in unruly actions in the House.

BJP would raise "important issues" and those relating to interests of the people, he said adding it would play the role of a constructive opposition.

To a question, he said there was a "lot of difference" between the NDA's agenda for governance and UPA's Common Minimum Programme (CMP) but did not elaborate.

Earlier breaking his silence over his party's electoral debacle, Vajpayee on Tuesday attributed the defeat to "complacency" and "failure to identify the rival."

"While in the battle field, the enemy is always identified, it was not so in this case," he said apparently referring to one of the party's campaign planks "Vajpayee versus question mark".

Vajpayee said 90 sitting MPs of the party had lost the election while there were others, who had served five to six terms have been returned. This showed that "there was need for the newcomers to learn lessons from this."