Merging companies have long seen Britain’s Competition and Markets Authority as something of an end-of-level boss. For two years running the CMA has blocked more deals than any other regulator, scotching ones like Meta’s acquisition of Giphy, a blameless meme-generator. This year it has been busy again, in April blocking Microsoft’s $69bn acquisition of Activision Blizzard, a video-game maker, which had looked on track for approval…