If TERROR! is the objective
Simple grenade/flare carried by radio controlled model
A couple of controllers for the 'terrorist cell' to take relay control from launch site to target. For the final leg you might want to modify the aerial for a directional signal on the controller and boost the power.
Crash plane and ignite grenade/flare in the middle of Trooping the Colour or the start of the London Marathon. If the final controller has a good enough view they might do a nice low pass trailing smoke to get better TV coverage and start a good chemical WMD panic.
That gets you all the headlines you could dream of for a couple of hundred pound.
Everything except the modified final controller and the flare/grenade could be bought easily at your local Maplins. I'm sure even the incompetents in Al-Quada UK could manage to make a flare or a firework explosion to scatter some highly visible powder around the target.
Biting the hand that feeds IT
