Last Friday Boris Johnson announced that he was resigning with immediate effect and wrote a long resignation letter. The press have announced that he has resigned.
However there is as yet no date announced for the by election!
It appears that he has managed to announce a resignation without actually formally resigning as an MP.
The UK has a very odd system for MPs. The can’t technically resign. Insead they have to apply for one of the nominal positions that disqualify them from being an MP.
In this case it does not seem to have happened. This is also true for the other two that announced their resignations the same day.
Correction:
He did actually resign on Monday
Developer Rants 