Boris Johnson is readying himself to make one of the most significant announcements of his premiership. Early next week he is due to either give the go ahead or halt the government’s development of a domestic vaccine passport. This is not about foreign travel. There is broad, but far from universal, acceptance that travel firms and foreign governments will stipulate some proof of vaccination status, or medical exemption, as a condition for travelling abroad. What the government has been working on behind the scenes goes well beyond that.