How much power did he actually have? He was leader, but lost the general. He could have reformed labour, and maybe they would still have had their landslide, giving Britain a more progressive government, but that's conjecture.
Or is this about his voting record?
All credible reporting I've seen is relatively certain that it was a small amount of military grade explosives.
If you have the device in front of you, and are prepping it for your secret operation, that also seems like a much more straightforward solution than trying to manipulate a lithium ion battery in a way that both allows it to work normally for years, but then explode violently enough to kill someone holding it.