There are, one must admit, things to be said against Boris Johnson, but his leading critics do not understand that their attacks assist him. On Tuesday in Manchester, Mrs May tried to upstage his arrival by claiming she had a new policy about post-Brexit immigration. She didn’t. The only person she upstaged was her Home Secretary, Sajid Javid, who should have been left alone to speak about a subject which, both by his job and his background, is his.