The important question being asked by our security services of tonight’s new video purporting to come from Al-Shabaab is whether it’s purely an aspirational rant or something more significant.
In it, a terrorist dressed in army fatigues asks: “Can you imagine what a dedicated mujahideen in the West could do to American and Jewish-owned shopping centres across the world”, before urging jihadists to launch attacks in London’s Oxford Street and Westfield shopping centre.
These are obvious locations that anyone who would want to launch mass casualty attacks in London is likely to have already considered. There's no evidence in the rambling video - more than an hour long - that the group is planning terrorism in Britain.
Al-Shabaab is on the slide - it appears to have little global infrastructure.
And it has little global ambition - its focus is East Africa. It’s no al-Qaida.
But there’s more to this. Shabaab is losing the war at home. Although they still control large parts of Somalia, an invasion by the Kenyan army has won back swathes of their former territory for Somali government forces.
Foreign fighters have fled. Once, 50 British nationals were said to be fighting with the group in Somalia.
Privately, Whitehall officials suggest that many have left - some for Syria - and some have been forced out.
Many observers have for a long time expected an "asymmetric response" from Shabaab - lashing out abroad to soften the blow from defeats at home.
The deadly siege at Westgate Mall in Nairobi, Kenya, might have been an example of this. But now they appear to have taken the lead from their rival Islamist franchise, the so-called Islamic State, by trying to motivate former fighters and sympathisers in the West to launch "lone wolf" attacks.
Two years ago, I was shown an al-Shabaab video in which a British fighter, speaking from Somalia, urged his countrymen to go to their local Argos to buy a device that could be used as a weapon.
But what then seemed like an unlikely form of terrorism - the "lone wolf" attack - has struck in western cities several times since.
Terrorist groups now make regular appeals for copycat attacks.
But this video is different. Although propaganda films frequently tell their followers what to do to launch an attack, they rarely tell them where to go.