MANCHESTER, England — He has been accused of inciting violence, misleading Queen Elizabeth II, running roughshod over the British Constitution and having a conflict of interest in his dealings with an American businesswoman.

But on Sunday, Prime Minister Boris Johnson of Britain was basking in the support of allies at the start of one of the most extraordinary conferences ever held by his governing Conservative Party.

That may have had as much to do with who is not at the conference in the northern English city of Manchester as who is.

The meeting is taking place in the absence of prominent party figures purged by Mr. Johnson for bucking him on Brexit; they tried to prevent Britain leaving the European Union without a formal agreement.