Factual error: The country of Pakistan was shown to be part of the G12 summit member countries. But the G12 are Australia, Belgium, Canada, France, Germany, Italy, Japan, Netherlands, Spain, Sweden, Switzerland, the UK and USA. (13 countries, but the name was never changed when Switzerland joined in 1984).
Continuity mistake: When English, Bough and his wife are looking at Garroch Castle from the submarine, Bough's wife says to English, "Jeremy has always spoken very highly of you." However, in the first Johnny English film, it was established that Bough's first name is Angus.
Continuity mistake: When the headmaster enters the classroom and asks the pupils where Johnny English is, English is not standing in camouflage against the wall, but he is doing so when the headmaster leaves.
Continuity mistake: When English gets in the driver's ed car, there's a cell phone on the console when he looks at the pedals on his side. When he steps on the gas, you see part of the console and now there's some sort of magazine that wasn't there before.
Continuity mistake: When Ophelia grabs Johnny English at the mansion, she pulls out a gun and places it to English's temple, but when the camera is behind him in the next shot, the gun is now much further up.
Plot hole: OK, a good laugh but why on earth deploy HMS Vengeance as a guard vessel to the G12 conference? Surfaced submarines are pretty exposed and useless against any likely threat, compared to a frigate or destroyer with SAMs, guns, small arms etc. And if the plot device is to have her launch a missile, Vengeance (as named and pictured) only carries torpedoes and Trident ballistic missiles, so hitting Volta's yacht with a missile wouldn't blow it up, more vaporise the whole area, even if it could attack something at such short range.
Answer: Because, it was time for a comeback, so they tasked Bough to complete the team.