Сoncerning Skripal case, you have to undeкstand that State Lies in western world (but also in the entire world) have always been weapons to manipulate the public opinion in order to convince it that an opponent state is a bad one and deserves to be fought.
When a state (UK for example) starts to lie, all services of the country work together for the same goal. All of them bring their contribution to the State lie.
In other words Police, Justice, Armed Forces, Foreign affairs, medias, Government ...etc, start to lie together in order to make the State Lie more credible for the UK and world public opinion.
In the Skripal case, it is obvious that the UK manipulation is made to put pressure on Russia and on Putin. It is linked to the Syria events. Pushed behind the scene by the state of Israel, which works in its own interests, UK (followed in the Skripal case by US, France and some others NATO countries) works very hard to maintain Syria in chaos. These countries (US, UK and FR)don't want the return of peace in Syria. They see a threat for the state of Israel if the peace is restored in Syria. They want to eliminate all opponents to the "deal of the century for Palestine" proposed by the duo Trump-Netanyahu. They want to cut Syria in pieces. So they put pressure on Putin to try to avoid a too strong Russian support to Syria.
I am not Putin but I am almost sure that he understands very well the game of the western countries including the role of Israel behind the scene. He is a very experienced leader for his country. He will likely take the right decision in pursuing his support to the legal Syria.
Today, NATO is strong in words, in telling nice stories to the people, in using medias to manipulate public opinions, in making noise but Nato is not very strong in Armed Forces. Its power declined a lot in the past twenty years. If Putin remains firm, NATO will leave Syria before the end of this year. Idleb must be cleaned. The victory on Daesh and Al Nosra is not negotiable.
Dont't forget that the pro-Israel lobbies are very powerfull in thesethree countries (US, UK and FR). AIPAC (American Israel Public Affairs Committee) in the US, CFI (Conservative Friends of Israel) in UK, CRIF (Conseil Représentatif des Institutions Juives de France) in France are the most influential lobbies in these three countries particularly in Foreign and Defence Affairs and in Intelligence Services.
Theresa May is a member of CFI. Most of the UK government members are also part of CFI. The three Head of States (US, UK, FR) were elected with a significant help of pro-Israel lobbies. Now they pay the price for this help. In return, they have to help Israel in maintaining the chaos in Syria. That explains the collusion between these three countries (USA, UK, FR)in the Syrian crisis.