Deutsche Welle: British Prime Minister Theresa May announced "drastic countermeasures” should Russia not account for the poisoning of ex-spy Sergei Skripal. The Russian government did not respond to the ultimatum. Having consulted with her security advisers, May has ejected 23 Russian diplomats from the country. Was that the right move?

WI: We know that when Russian diplomats are kicked out of Britain, then British diplomats get kicked out of Russia. It's tit for tat. Both sides feel the effect. Or not.

Then there is the question of if and how much this process can be corroborated to provide the UK's partners with more or less enough certainty to share in the British findings and say: There is clear Russian responsibility or at least partial responsibility. If so, and I assume it is the case, the question emerges: Can the UK's partners – that is, the EU – form a unified front? Is there even a possible common NATO response? It was my impression on Wednesday morning that at least the European Parliament was not quite ready to definitively say: This is the case, and therefore we are acting on that basis.

DW: Is that to be expected?

WI: I assume there are discussions underway that hopefully lead to at least a half-way united front so Great Britain is not left alone in dealing with this matter. But I am skeptical that the matter will somehow resolve itself in the near future. I'm skeptical for a number of reasons, in particular because the Russian presidential election is just days away. That gives Russia even less cause to submit to grand public explanations or cooperate with the British government.

DW: Other sanctions are also on the table, such as financial sanctions. Would these impact Russia more?

WI: When it comes to financial sanctions there is the immediate question of who they effect. British measures, I'm afraid, would be nothing more than shooting yourself in the foot. The city of London would likely suffer as much as Russia. If only Britain takes action, then the Russian side would seek out non-UK banks and financial institutions. So the question is: Rather than bilateral sanctions, wouldn't more broadly coordinated action make more sense, at least at the EU level and with NATO?

DW: Given all these possible alliances, what role does Brexit play?

WI: None initially because the UK is still a member of the EU. And for as long as it is, both the UK and the EU will afford the other necessary loyalty. The UK remains a full member of the EU, meaning Article 42 of the Lisbon Treaty remains in effect: the solidarity clause. Member states must come to the aid of another member state when threatened. The question is if it is abundantly clear that a state actor was behind this. And if so, presumably Russia, is the evidence beyond any reasonable doubt? These questions are for me not yet sufficiently clear.

DW: The entire debate mirrors the one in 2006 when Alexander Litvinenko was murdered, which is when you were Germany's ambassador to the UK. What was the experience then? There were sanctions imposed and diplomats ousted at that time, too.

WI: That's right, but the sanctions were mainly bilateral. And after some time enough of it was swept under the rug and relations returned to normal.

However, British-Russian relations have been sluggish ever since, and the UK's Russia policy has been kept on the back burner. That policy was most of all successful in bringing a lot of Russian capital into the city of London as well as many well-to-do Russians. A lot of Russian money poured into London, which leaves the British side asking itself: How much do we hurt ourselves with possible bilateral sanctions?

In other words, it is not an easy situation, and I do not envy Theresa May's government in finding the best way to deal with this question.

DW: How dangerous is the tension between Russia and the UK for the international community?

WI: I think it's terrible because relations have already been at a low point for a long time. There is already a massive trust deficit, and that trust is even further damaged with the suspicion that Russia was behind the attack, tolerated it or was negligent in letting it happen.

I see ever less of a future in being able to try to rebuild trust with Russia. The consequence would be even lower chances of discussing arms control, military cooperation and a solution to the Donbass conflict. We are playing with fire, and I hope that it is also clear to the Russian side that this is not in its interest. Diplomacy's greatest asset is trust, and that is getting ruined here.

The interview was conducted by Michael Borgers.

Wolfgang Ischinger is a diplomat and security expert who has led the Munich Security Conference since 2008. He has served as Germany's ambassador to the US and UK.