London-based terrorists tried last year to buy half a tonne of toxic chemicals with the aim of killing thousands.

Their plot came to light when the supplier became suspicious about the quantities of chemicals involved. . . .

The effort to buy the saponin was in some ways inept. Apart from the quantities that were ordered – 500 to 1,000 times the normal order from a university laboratory – the explanation for the planned use of the product was also incredible.

The group described its intended use as “a fire retardant on rice intended for human consumption”.

Traces of ricin were found in a police raid on a north London flat in January.

Seven people were arrested and four of them later charged with possession of articles of value to terrorists and with being concerned with the production and development of a chemical weapon.

The ineptitude is comforting. The effort isn’t.

UPDATE: A couple of readers correctly note that the 1993 attack on the World Trade Center was inept, too. That’s right. These guys aren’t especially bright, but they’re persistent, and they learn from their mistakes, which is enough to make them dangerous.

ANOTHER UPDATE: Reader Mark Draughn notes this story from USA Today about the way in which the inept 1993 attack led to improvements in safety and evacuation that sharply cut the death toll in 2001. Scroll down to the “lessons learned from terrorists” section. Yes, learning is a two-way street — or it had better be. I wrote something on that subject here.