An interesting article at the Register explains the perils of trying to mix up chemicals to make bombs.
Someone I used to know told me years ago about how to make this particular explosive. He also warned of the difficulty. In fact, I seem to remember the advice was "do it in your shed" and "if it's temperature rises above (something) - run like f*ck!".
So the questions remain: Is the threat real? Are our intelligence and security services inept? Why do our politicians understand as little about terrorism as we do?
Update: Liquid bombs are of course not new: See Flight 434