The 37-page document detailed rule-breaking parties in and around Downing Street during the pandemic.
Her inquiry found that many of the events "should not have been allowed to happen" and that staff who raised concerns were not treated with respect.
Mr McNally said: “Sue Gray’s report is shocking, and lays bare the sheer contempt those in Downing Street had for the Covid restrictions we were all ordered to follow.
“We now see proof that staff actively arranged parties, despite warnings they’d be in breach of the rules, and there were even boasts about them ‘getting away with it’ afterwards.
“Some of the photographs make Downing Street look like a drinking den. Individuals were sick, brawling, and partying, before leaving hard-working security and cleaning staff to clear up the mess.
“The country deserved so much better during such difficult times. So many of us experienced the pain of losing friends and loved ones in Falkirk. This report was incredibly hard to read with this in mind.
“The idea that Boris Johnson thought all the rules were followed is contemptible – standards have deteriorated on his watch. He feigns sincerity when he apologises for his pitiful behaviour, while others in his team have lost jobs because of his inability to be a leader. He must accept the ultimate responsibility for what went on.
“The only honourable thing he can now do is resign.”