Last Friday, Michel Barnier gave a stark warning about the lack of progress in the Brexit negotiations, but this week Boris Johnson has returned to work. Perhaps it was unrealistic for Barnier to have expected the UK to have engaged seriously with the trade-offs and concessions essential to a long-term agreement while the UK prime minister was ill.Brexit is Boris Johnson’s big thing. He made it. Other Tory ministers have no leeway to make Brexit decisions without his personal imprimatur. He has purged from his party all significant figures who might advocate a different vision of Brexit.