Have you paid any attention to Russia's meatwave tactics in Ukraine that so far already piled up half a million of Russian casualties?
If you did, you wouldn't be considering this scenario implausible, because we see videos of said Russians needlessly marching towards their deaths on a daily basis.
I'm not saying it not possible, but the fact that there isn't a rather more concerted response involving, say, the SBS or an encounter with an Astute within the last several weeks while it's been tooling around the North Sea implies that the intelligence services don't consider it as much of an actual active threat as the media circus wants it to be.
Certainly if there was even a breath of Russian military on the ship, I don't think "hey sure, just drop anchor outside Margate and chill next to these other ships and right by the Thames and Channel shipping lanes" would be the call they'd make.
The people Russia is sending to their deaths in their meat wave tactics aren't exactly Russian military either. They are at best civilians under contract and moved to front lines weeks if not days after being hired.
Then there are the civilians pressed into service such as unsuspecting immigrants and Ukrainians who found themselves in occupied territories.
The key factor is complete disrespect for those under your control, and willingness to sacrifice themselves for the smallest reason.
Margate may not be luxurious, but it's not a Ukrainian front line.
The only evidence that it's anything other than a damaged ship in a shit situation (even shitter than your average Syrian/UAE cargo ship, which is probably saying something) with a very low chance of a very big explosion, trying to find somewhere to put in, is that the word "megabomb" makes good headlines and people want to have exciting things happen, even if "it" is blowing up a town, no matter how dreary, from 12 miles away with what would presumably be the biggest non-nuclear explosion in history.
https://www.ft.com/content/b9396112-585a-4f7e-9628-13d500c99...