A country that supports one of 2 countries cannot protect its diplomats.

Russia has revoked the accreditation of six British diplomats, accusing them of espionage. The reason is that the diplomats are trying to incite the military situation in Ukraine against Russia.
The FSB said that the documents show that diplomats in Moscow helped coordinate the ‘escalation of the military situation’ in Ukraine.

The government has not reacted seriously to Russia anyway. In fact, Britain and other Western countries have been providing arms and money to Ukraine since the beginning of the war. Even if the diplomats of these countries were in Russia, it was not possible for them to be neutral. Most likely, they were both providing information to Ukraine and helping in many ways.

When a government openly supports one of the two warring parties, its diplomats are the primary providers of that support.

So it is not a big surprise that Russia has revoked the accreditation of six diplomats. Diplomats from other countries may follow suit. Russia has a list of diplomats from the following countries.
USA
France
Germany
England
Austria
Canada

In such an environment, it would be stupid to protest Russia. You will provide weapons and aid to one of the two warring parties and at the same time expect Russia to congratulate you.