I think that was polonium, not plutionium, and he did show signs of radiological poisoning so i'm not sure about that one at all. Not that plutonium would not kill you, but it's so poisonous you might die well before the radiological effects kill you
As for things like phones, watches and such spying on you: There is no need to panic over that. It certainly is possible to do that, but it's also detectable. You can monitor their network traffic and see if they are sending data somewhere when they should not. If they are used as live listening deviced you would expect a stream of a certain bitrate to go somewhere unusual.
A smarter approach would save the audio data and transmit it at some random point later, possibly coinciding with something like opening the browser, facebook, or something else that generates a shitload of data traffic. It could still be analysed though.
When connected via wifi it's very easy to analyse these signals, you need nothing more than some free software and possibly a wifi dongle to set up a wifi network to connect to and monitor.
Something similar can be done for 2G/3G/4G networks though the equipment is more expensive. If it involves UK politicians this stuff is easily available though, just test what is sent using an imsi chatcher or get cooperation from the telco.