The issue is simply whether or not Johnson deliberately lied to Parliament. If the committee finds Johnson lied, the ex-PM could be suspended from the House of Commons and voted out of office in his Uxbridge constituency.
“Partygate” is about the fact that during the corona pandemic, lavish parties were celebrated in Downing Street 10 when this was prohibited by the lockdown. Johnson assured Parliament that the Corona rules were being followed at his official seat. The committee released extensive evidence on the parties on Wednesday.
Johnson’s defense boiled down to the fact that while he misinformed Parliament, he acted “to the best of his knowledge”. He had no knowledge of the extent of the celebrations at the time.
The committee will probably decide after Easter whether or not to believe Johnson’s protestations. In British parliamentarism, lying to MPs is considered one of the worst misdemeanors.