@ToraToraTora
Nukes have a kind of "minimum size", due to the required critical mass and all the mechanism required to make it go off. The Trinity test device and the Hiroshima/Nagasaki devices are about as small as it gets. So a vehicle capable of shifting a 6ft sphere, weighing a ton or two, would be the minimum. No drone can lift that much, yet and any truck has to make its way here without setting off detectors.
Hence the emphasis on a dirty bomb. The question, there, is "do they want to wait 25,000 years to be able to claim any landholdings in the target zone or not?"
If they wipe out all the prime farmland in Europe and then climate change turns the levant into an extension of the Sahara, what the heck are they going to eat?
More to the point, where is their food coming from, right now? Who, in their right mind is still farming in Syria and Iraq?
Footnote:
Given the magnitude of foreign investment in London real estate, several nations will come down on them like a ton of bricks if extremists tried anything there. Although the Saudis seem to have left their mansions to go derelict and probably go to Dubai to do their shopping, rather than Harrod's.