The campaign to prevent Britain leaving the EU, such as one exists, is not being led by a charismatic politician from Britain, nor even by wistful Eurocrats in Brussels. Instead, the standard-bearer of the anti-Brexit charge -- at least while the UK Parliament is on its long summer break and Prime Minister Theresa May is walking in the Alps -- is little-known former political apparatchik vacationing on a Mediterranean island at the other end of the European Union.