How plausible is this alternate theory of the UK Russian spy poisoning?

Here's the theory: Back in the 1980s, the Soviets provided the nerve agent to one of the governments in the Middle East, perhaps Libya. During a recent conflict, the facility where it was stored was captured by ISIS or some other terror group and the poison fell into their hands. The terrorists targeted a known Russian spy in England to stir up an incident between the West and Russia, ideally to spark a conflict wherein the two biggest enemies of ISIS fight each other. .... .... ... ... ... ... . Terrorism is asymmetric warfare, you should expect the unexpected. ....... .. ... ... ... ... ... ... ... .. ... ... ... Of course this is just a theory, but what do you think, is it plausible?