If we had a bat signal around here, this story would earn it.

Iranian Revolutionary Guard forces have been spotted by British troops crossing the border into southern Iraq, The Sun tabloid reported on Tuesday.

Britain’s defence ministry would not confirm or deny the report, with a spokesman declining to comment on “intelligence matters”.

An unidentified intelligence source told the tabloid: “It is an extremely alarming development and raises the stakes considerably. In effect, it means we are in a full on war with Iran — but nobody has officially declared it.”

“We have hard proof that the Iranian Revolutionary Guard Corps have crossed the border to attack us. It is very hard for us to strike back. All we can do is try to defend ourselves. We are badly on the back foot.”

Have the Iranians judged the strength of the British military based on its most recent close encounter with the Royal Navy? If so, now’s a good time to start worrying.

Update (AP): The Sun’s article is out. I’m suspicious that a story as potentially big as this is being leaked to a tabloid instead of one of the prestige papers, but here you go:

IRANIAN forces are being choppered over the Iraqi border to bomb Our Boys, intelligence chiefs say.

Military experts claim this worrying move means we are at WAR with Iran in all but name…

Our Boys picked up the Iranian helicopters on radar crossing into empty desert.

The sightings have been confirmed to The Sun by very senior military sources.

At least two Brit squaddies are thought to have been killed by bombs planted during these incursions into Maysan province — Corporal Ben Leaning, 24, and Trooper Kristen Turton, 27…

Until now, secret units from Iran’s fanatical RGC have restricted themselves to just training and arming Shia rebels in Iraq.

Why are they choppering in to plant bombs? They own southern Iraq; they could just send the materiel across the border and let their proxies do it for them. And why would they risk trying something as provocative as this with the Brits having already declared their intention to withdraw and the U.S. on the brink of following suit? They’ll have a free hand in Iraq once we’re gone. It’s madness to chance a casus belli with a direct attack on coalition troops.

I guess it all depends on how mad you think the mad mullahs are. Not as mad as has been suggested, perhaps.

Update: Bob Owens checks around with a few people who would know and discovers that the Maysan province story smells funny.