ITV News' UK Editor Paul Brand discusses what this could mean for the former PM
There is one main admission in Boris Johnson's evidence - he did mislead MPs over Partygate.
So why the need for an inquiry? Well, what he disputes in his submission is that it was either done intentionally or recklessly.
None of that is new. In fact, very little of the evidence comes as any surprise. But what we now have is the full argument that Mr Johnson intends to deploy when he faces MPs tomorrow.
In essence, there are three key elements to consider:
He is adamant the kind of gatherings that took place in No10 were necessary for work
Mr Johnson references the old and creaking building where Downing Street staff were crammed in trying to save the country from the worst pandemic in a hundred years.
It was inevitable that at times they would need to gather together in the national effort, he argues. But all of it was absolutely necessary according to the former prime minister. We've heard this many times before, but it is nonetheless key.
He was advised at every stage that the parties had been within the rules
Here's where we get some new, though highly contested, evidence. Mr Johnson provides WhatsApp messages from the time, where he is told by his advisors that he should tell Parliament no rules were broken.
MPs will no doubt counter those messages with other texts from the time, in which advisors admit that they're struggling to come up with justifications for some of the events - though Mr Johnson says he was never sent them.
So, if he thinks it was necessary for staff to get together in No10 - and he insists he was told all the way through that no rules were ever broken - why might MPs on the Committee still believe there is scope here for him to be deliberately misleading them?
Mr Johnson has a pair of fully-functioning eyes
What the Committee argues is that it is simply not credible for him to have attended events and not realised that they were contrary to the rules at the time, given what he saw before him.
Consider this comparison: If a nurse, teacher or supermarket worker had gathered with their colleagues, drinks in hand, food on a table, closely packed together after what most people would view to be the usual working day, what would their boss have done if they had walked in?
Well, in Mr Johnson's case, he joined the event. Never for long, he insists, and always before any of the events became raucous. But nevertheless, he surveyed the room and saw the scene and still concluded that it was completely reasonable.
He asks why, if he'd truly believed that rules were being broken, would he have allowed No10's official photographer to take pictures? But stranger things have happened and not all leaks are foreseen, otherwise very few would ever make their way into a journalist's hands.
Overall, Mr Johnson's submission lays the ground for an almighty showdown with MPs.
At the heart of it will be the question of his credibility. He must put in the performance of his career in order to convince the Committee that in misleading Parliament it was either his eyes or his staff deceiving him, rather than him deceiving MPs.
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