At the right doses, nerve agents can kill within five to 15 minutes, says chemical weapons expert Mark Bishop at the Middlebury Institute of International Studies at Monterey. But the Novichok agents are thought to be even more dangerous and deadly; Mirzayanov claims that Novichok-5, for example, can be five to eight times more potent than VX. So the fact that the Skripals are still alive means that “it must have been low dose, or impure, or not administered in a really efficient way,” Bishop tells The Verge. “Because it doesn’t take very much of a nerve agent to be fatal.”
Make of that what you will (and we still have no independent verification of the given analysis)

It has been a convention to date(pre-polonium days)that you do not go after exchanged persons, and you do not endanger the civilian population. No longer true if the sheeple believe everything they are fed.

It all makes as much sense as Assad supposedly gassing civilians when he has virtually won.

https://www.theverge.com/2018/3/14/17120696/russian-novichok-skripal-nerve-agent-chemical-weapon-poisoning-england