As tankers carrying hundreds of millions of dollars worth of Russian oil pass through British waters, a Sky News expert warns we are heading for "militarised confrontation at sea".
In the English Channel, less than two hours by fishing boat from Dover, some of the most potent weapons in Russia's war on Ukraine are hiding in plain sight.
On a misty February morning midway between Britain and France, we watch tankers carrying Russian oil worth around $100m (£74.1m) cruise past in defiance of Western sanctions, embargoes, and price caps.
Dozens of these vessels pass through the Channel every month, part of a "shadow fleet" of up to 800 vessels that have kept the oil revenues that fund the war on Ukraine flowing.
This week, the UK government announced fresh sanctions against the Russian oil trade but the evidence of a day on the water is that the shadow fleet operates with apparent impunity, right under the nose of Kyiv's allies.
Our skipper, Matt Coker, usually takes sea fishing parties out on the Portia, but we were after a bigger catch; three vessels in the shadow fleet carrying oil from Russia's Baltic ports.
He says they are a routine sight in the world's busiest shipping lane: "When you see these Russian ships and these oil tankers, you know, it's a regular occurrence. To be honest, no one really takes any notice."
We had tracked the tankers - the Rigel, the Hyperion and the Kousai - from the Gulf of Finland, where they had been loaded with oil at Russian Baltic ports, to intercept them as they passed the narrowest point of the Dover Straits.
Up close in a rising swell, the scale of the vessels is unavoidable, and each one tells a story about both the impact and the limits of Western action.
The Rigel, a Suezmax-class tanker, is more than 270 metres long and fills the near horizon as it emerges from the mist. With a capacity of one million barrels, its cargo of oil, loaded a week earlier at Primorsk, is worth around $55m (£40.7m).
It is sailing under a Cameroon flag, owned and managed by a company in the Seychelles, and sanctioned by the EU, UK and Canada, among others.
That prevents it from using port facilities in any of the sanctioning countries, but not from heading to its next known stop, Port Said at the head of the Suez Canal. We cannot know where its oil will be unloaded, but since the invasion of Ukraine, the bulk of Russian oil has been sold to China and India, at a significant discount.
The flag switching tactic
As recently as December, it was sailing under a Sierra Leone flag when, after making a delivery to Venezuela, it switched flags and evaded the US naval blockade in the Caribbean.
Switching flags is a routine tactic in the shadow fleet, opaque ownership is common, and insurance cover is often unclear, a serious concern given many of the vessels are ageing and poorly maintained.
The US has taken direct military action against tankers in the shadow fleet linked to Venezuela, with at least seven seized since last year, the most recently in the Indian Ocean on Tuesday.
French paramilitaries also seized a vessel in the Mediterranean last month, but despite the almost daily passage of shadow tankers through the Channel, direct British interventions so far have focused on insurance.
As we watch the passage of our third sanctioned tanker, the Kousai, we overhear a message from the coastguard to its captain on the open VHF radio channel, demanding proof of insurance.
The captain is asked to email documentation to a government email address within 24 hours. We do not hear the Kousai's response, and in a matter of minutes, it too has passed.
A reaction to sanctions
Sanctions against Russia's oil industry have had an impact, reducing the value of Russian oil if not the volumes that it moves.
The growth of the shadow fleet itself is a market response to tightening sanctions. With the majority of western-controlled tankers and associated marine services beyond Russia's reach, it turned to an ad-hoc, opaque collection of older vessels to move oil, often covertly.
"Over 60% of Russian crude is being exported on the shadow fleet," says Pamela Munger, head of European market analysis for energy analysts Vortexa.
"You have more vessels that need to be in the chain. Let's say a sanctioned vessel loads Russian crude and let's say it's on its way to China.
"It could make up to five, six, seven ship-to-ship transfers along the way in order to disguise the origin of the crude and move it on to… Non-sanctioned vessels, which it will eventually discharge into its end buyer."
