Tim Farron MP has echoed calls for the Prime Minister to resign if he has been found to have broken lockdown rules and misled Parliament.
Boris Johnson is under renewed pressure to step down over claims that he flouted lockdown regulations by attending a party in Downing Street on 20 May last year.
The Prime Minister has apologised after admitting attending the party, but claims he thought it was a work event.
"There is no doubt that this is a resignation matter, yet the party in power is treating Parliament with as much contempt as they are treating the people," said Farron, who is a Christian, on social media.
In another post, he added, "Maybe we now understand better why the PM stood by Dominic Cummings over the Barnard Castle trip ... after all, what DC was accused of was a trifle compared to what the PM had done... and DC knew it!"
Cummings, Johnson's former chief adviser, claimed last week that there had been a drinks event at No 10 last May. The claim appeared to be backed up by an email from a senior Downing Street official leaked to ITV News.
The email from Johnson's principal private secretary, Martin Reynolds, is reported to have been sent to over a hundred Downing Street staff, inviting them to a garden party during lockdown and telling them to "bring your own booze".
MSP Murdo Fraser, a member of the Conservative Christian Fellowship, has backed comments from the leader of the Scottish Conservatives, Douglas Ross, who said the Prime Minister "must resign" if he has misled Parliament.
"If he has breached his own guidance, if he has not been truthful then that is an extremely important issue," he told Sky News.
"As I've said previously, if the Prime Minister has misled Parliament then he must resign.
"People are furious, I'm furious. People across Scotland and across the United Kingdom are furious.
"This email went out to about 100 people inviting them to a party when no one else was allowed to do that, in fact, the government guidance was very clear in England that you could only meet up with one other person from another household.
"I can understand the fury, the anger and the rage."
Fraser, Tory MSP for Mid-Scotland & Fife, responded on social media with: "Well said, I agree."
A snap poll by Savanta ComRes shows that two thirds of UK adults believe Johnson should resign over the allegations, while just under two thirds (65%) say Reynolds should also resign.
Over three quarters (77%) said the Met Police should formally investigate any alleged breaches of Covid restrictions at No 10 on 20 May, while even more (86%) feel the public have been let down by the scandal.