Pass through many channels is regulated by international treaties. English Channel, Dannish Baltic entry straits, Bosporus, etc are included. Generally, military ships are allowed, but have to notify N days in advance (N = 3, 7 maybe more sometimes) and submit a plan and description.
Russian rust buckets seemed to not violate anything when passing English Channel, othersise they would have been blocked, stopped, etc.
In a similar way the Ukrainian ships should have notified Russia in advance. BTW, there is only a 24 hr notice applicable there. And they (Ukr. ships) did it before no problem. But this time they decided to "test" (or were advised to test by their supervisors). Test failed.
Imagine that a person who has an entry visa to UK tries to rush through a passport control without showing his/her docs. Just saying that he has a right but ignore (f...) the routine procedures. Also pointing a gun towards immigration and police officers. Would be surprised if he would not land behind the bars.