An ambassador, in the well-worn phrase, is an honest man sent to lie abroad for his country.

Like many maxims, it contains more than a nugget of wisdom: duplicity and bluff are vital elements of diplomacy. That begs a painful question for the EU. Given that it will be hard for ambassadors from the new European External Action Service (EAS) to lie undetected, what kind of envoys will they be?

It will take some months for the final shape of the EAS to emerge. Since the Lisbon Treaty came into force last December, rival bits of the EU machine have been fighting like stoats for control over the Union’s new diplomatic service. Nonetheless, many Brussels insiders remain rather excited by the thought that Europe will soon run one of the world’s largest diplomatic networks, boasting embassies from Uruguay to Uzbekistan.

Here is a prediction: the EAS will turn out to be a disappointment. The near-impossibility of the EAS telling third countries a decent fib is just one (richly symbolic) reason why.

Most EU countries do not really have foreign policies. They have neighbourhood policies, which may or may not drag them into some nasty spats that make little sense to outsiders. Inasmuch as they have diplomatic networks, they are designed to extract the maximum advantage from relations with a handful of big powers, like America, Russia and China. Some may have former colonies, where they can play at being superpowers (like Belgium in Congo). Others (such as Cyprus) see foreign relations as tools for advancing a single, overwhelming national interest.

For most European countries, the idea of EU embassies taking over their minimal interests around the rest of the globe sounds both cheaper and more politically rewarding than going it alone. The logic is clear enough: why, for instance, does Hungary maintain an embassy in Peru?

In contrast, a minority of EU countries have ambitions to be something like great powers: either globally, like France and Britain, or regionally, like Spain in Latin America. Finally, there are important countries with lucrative foreign interests to defend, even if they do not have strategic visions to promote: think of Germany’s ties to Russia, or Italy’s snuggling up to any number of energy-rich despots.

All these groups – the tiddlers, would-be global players and cynics – will undermine the EAS. As soon as the stakes rise high enough, someone will always see an interest in breaking ranks.

Some years ago, when this reporter was posted to Beijing, a European diplomat groaned at having to attend strategic meetings of EU member states, hosted by the country holding the Union’s rotating presidency at that time. Diplomats were required to clamber into a high-security box suspended on ropes from the corners of a strongroom in tha......