The opposition bloc vote which almost resulted in defeat for BN last night was a surprise to many MPs, including those from Pakatan MPs, said Amanah lawmaker Khalid Samad.

"The ambush in Parliament last night went well. No one expected that we would do a bloc vote.

"It is not just the BN MPs who didn't know, but some Harapan MPs didn't know either. It had to be that way," the Shah Alam MP said in a Facebook post.

Khalid said if all Harapan MPs knew about the plan and stayed on, the BN side would have suspected something.

He added that the absence of some Harapan lawmakers lulled BN into a false sense of security, prompting many of them to leave Parliament.

When the bloc vote was called, the Amanah communications director said only about 40 BN MPs were in the House.

Last night's vote was called during the committee stage debate of the Domestic Trade, Cooperatives and Consumerism Ministry's portion of Budget 2018.

BN narrowly survived the vote by a razor-thin margin of 52-51.

Harapan was aided by six PAS MPs who also voted against the federal budget. Two PAS MPs, however, abstained from the vote.

Also not present in the House at the time of the vote were 26 Harapan lawmakers.  

Khalid said those who had left the House had other affairs to attend to and were not playing truant.

However, it is not clear yet who the 26 absent MPs were.