The prime minister snubbed MPs demanding a simple answer to claims he attended a party in the Downing Street garden during Covid lockdown.
Boris Johnson sent a junior minister to the Commons instead to face angry calls for his resignation.
SNP Westminster leader Ian Blackford appealed to Mr Johnson’s own part to oust him.
An email published on Monday evening showed 100 staff were invited to bring a bottle to drinks in the garden on May 20 2020 while ordinary members of the public were banned from socialising in groups outside.
Did he attend?
Labour secured an urgent question at Westminster on Tuesday hoping Johnson would set the record straight over the party row.
Conservative MP Michael Ellis was heckled relentlessly by opposition members as he tried to respond for the prime minister.
Mr Ellis said it “would not be appropriate” for him to comment on an ongoing investigation led by Sue Gray – again refusing to quickly confirm if Mr Johnson was there on not.
He repeatedly refused to say “yes or no” to increasingly irritated MPs.
And he would not say if the prime minister had told him privately if he’d attended.
The Prime Minister’s official spokesman earlier said he would not comment on the parties saga while the probe is under way.
SNP Westminster leader Ian Blackford said: “The harsh reality is that people round these islands watched loved ones dying, and missing funerals, and the PM and his staff partied behind the walls of his private garden.”
Mr Blackford said: “The Prime Minister should be here to answer these serious questions. Where is the Government frontbench, and indeed where is the Government backbenches?”
He can run but he can’t hide.
– Labour deputy Angela Rayner
He added: “If he won’t do the decent thing and recognise that he ought to resign, I say to the minister and I say to the Conservative backbenchers that they are going to have to do what the Prime Minister has failed to do and force him from office, and do it now.”
Labour deputy leader Angela Rayner said Mr Johnson’s absence from the Commons for the urgent question “speaks volumes”.
She said: “I think his absence speaks volumes as does his smirks on the media, the public have already drawn their own conclusions. He can run but he can’t hide.”
Conservative former minister Sir Christopher Chope asked: “Why can’t all the dirty linen be washed at once? Why are we getting this drip, drip feed of parties?
“Surely the civil service must have known that there was a party on May 20 and they should have referred it already to the inquiry.”
Mr Ellis, in his reply, said: “We have a number of dates that have come out at different times and that will, presumably, have an effect of delaying matters.”
Mr Johnson is expected to be in the Commons for Prime Minister’s Questions on Wednesday.