Then determined bombers will make deals with like-minded farmers, or organize a group of like-minded persons to buy smaller quantites across many vendors and time periods so as to avoid raising the red flags. It is a fatal conceit to assume that this is the reason that car bombs have reduced in the UK. It may, or may not, be a contributing factor. Much more likely is that the effectiveness of UK police in undercover operations has identified those who would pursue such tactics and delt with them already or that the grievences against the UK have either been resolved or overshadowed by the grievences against the US and Israel. Or just simply that the population of would be bombers still free and alive to do such things has been reduced. Most likely a combination of all these factors, but corrolation is not causation.
With respect, this is not something we need to debate. It worked. Immediately. The bombers didn't go away and when Libya sent supplies of Semtex they were a nightmare again. But fertiliser based bombs were dealt with.
It demeans your logic when you try to ignore facts. Just saying....
Present your facts, or they didn't happen.