Leading article: Watch out for more warning shots

A peculiar whiff trails behind the latest claims about Iran's involvement in attacks on British forces in Iraq. As though out of nowhere, we suddenly have an unnamed "senior British official" accusing Iran of making contact with insurgents and supplying explosives. The allegations go all around the houses: they are indirect in that they imply many links in the supply chain, but they are direct in their inference that Iran is responsible for the death of British troops. No proof is offered in support of the claim, but Mr Blair signed up to the general idea yesterday, albeit cautiously.

This is hardly the first time that Iran has been implicated in the Iraqi insurgency. Almost from the moment the occupation started to go wrong, US and British officials preferred to blame outside intervention rather than accept the reality of a home-grown resistance. They have strongly hinted at Iranian involvement, even at local cross-border incursions. At various times, they have accused both Abu Musab al-Zarqawi and Muqtada al-Sadr of having active links with Iran, but not for a while.

One explanation, offered by supposedly baffled officials, is that by supplying the insurgents, the new Iranian government might be flexing its muscles. It might be trying to warn the US and Britain of the escalating cost of their Iraqi involvement. Or it might be trying to signal that attempts to influence Iran over its nuclear policy have a price. But there could be quite a different motivation. Either way, the initiative for upping the ante would come from Iran.

But there could, of course, be quite a different explanation. The relative British silence over Iranian involvement in Iraq coincided with the protracted nuclear negotiations between the European "troika" and Iran. Those talks are now over and the issue is on its way to the UN. Meanwhile, the British have run into difficulties in the once-peaceful Shia south. Who now has the greater interest in putting pressure on whom?

Iranian intervention of any kind in Iraq, but especially the supply of weapons or explosives technology, could be deemed aggression. From there, it is not hard to imagine "justified" retaliation in the form of a US or British air raid or two. That such a raid might be directed at one or other of Iran's nuclear research facilities could not be excluded.

For the time being, the accusations against Iran are more likely to be a warning shot, more a signal of the changing mood, than a prelude to war. Any new charges, though, are worth watching. Unnamed senior officials dropping convoluted hints about another country's bad behaviour smacks of media manipulation. Remember the 45 minutes and those weapons of mass destruction? We must not forget them.