No one should be in any doubt. The way the Iranian authorities have singled out Iranian employees of the British embassy for their hostile attentions shows that they have identified a vulnerability in Britain's defences that is entirely of our own making. So-called "local hires" have become more and more the norm in our embassies, not just in Iran, but in many other countries, and this has consequences, many of them unwelcome.
It was, for instance, Russian employees who bore the brunt of Britain's stand-off with Moscow over the British Council two years ago. It was they who were called in to explain their tax affairs to the Russian authorities in the early hours of the morning; they who were harassed on their way to and from work. The Iranians are capitalising on the same weakness.
The advantage of recruiting locally is clear: to put it bluntly, local hires are cheaper than Britons. They are already there, they do not need air fares for themselves and their families, nor school fees for their children, nor the whole expensive ex-pat package. And their wages, while respectable by local standards, will be lower than those of British employees.
Other reasons will be cited in favour of recruiting locals, including their familiarity with the language and culture of the country. And it appears that at least some of those at the Tehran embassy, including several of those singled out by the Iranian authorities, were in the political section, working as analysts and translators. Lack of sufficient British expertise in these areas may be used to justify such recruitment.
There was a time, though, when foreign nationals were taken on only for relatively menial duties, mainly housekeeping and maintenance, not for what might be called "white-collar" jobs. And while there are plenty of instances of maids and others moonlighting for their home security services in Eastern bloc embassies during the Cold War years, there was, or seemed to be, a very clear division between the sort of jobs open to "local hires" and diplomatic, consular and analytical posts that were not.
That distinction seems to have been progressively lost. I am sometimes amazed to find nationals of the country concerned working, say, in the consular section, checking applications from their compatriots for visas, or in highly responsible analytical posts, essentially assessing their own country for the benefit of a foreign power. And I have often wondered, first, how far this reflects a lack of home-grown British expertise and, second, whether it is a particularly good idea, even when the recruits are from fellow EU countries. If, Britain is as sensitive about its sovereignty as it is, should we be relying on others to conduct analysis that is in our national interest?
But there is another aspect, too. Our reliance on local recruits has implications for these individuals, too, and it can be extremely unpleasant, as the experience of the Russia employees of the British Council and now the embassy staff in Iran shows.
Their motives in joining a British government concern may be various: decent pay and conditions, contact with Westerners and an outlet to another world; the chance to use their qualifications or improve their English. But if diplomatic relations deteriorate, they can all too easily be accused of being in the pay of the enemy, working for a hostile power.
From their home country's perspective, that is no distortion: this is precisely what they are doing. Nor do the difficulties stop there. When relations become seriously fraught, as they have done with Iran in the aftermath of its disputed election, not only do locally recruited staff find their loyalties divided – between their country and their paymaster – but Britain's interests are directly jeopardised.
First of all, and understandably, local staff may not turn up to work. Where the local staff outnumber Britons by three to one, as they appear to in the Tehran embassy, this must seriously affect its work, and the effectiveness of British diplomacy. Second, Britain finds itself effectively saddled with hostages taken by proxy. Those concerned are not British citizens and they do not enjoy diplomatic immunity. So Iran – or Russia – can harass or detain them with impunity. But they surely impose a moral obligation. They also expose an enormous vulnerability that was just lurking there, ready to be exploited.
Maybe we wanted to punch above our weight in diplomacy, but we are asking other people's citizens to help us do so. The result is both their loss, and ours.