Putin is about to declare war on the whole world

British military intelligence reported yesterday that Russia’s Black Sea fleet may be planning a naval blockade of Ukraine, in which it might intercept and seize merchant vessels travelling to and from the embattled nation. The most obvious impact of this would be to interdict Ukrainian grain exports: Russia recently withdrew from an agreement under which it was permitting such exports to continue, and has been hitting Ukrainian ports and grain storage facilities with missile strikes.

Can Russia mount such a blockade?

Not completely. Grain ships need to travel between Ukrainian ports, the main one being Odesa, to the Bosporus strait in Turkey and so gain access to the world’s oceans via the Sea of Marmara and the Aegean. The Black Sea Fleet would probably not care to operate close in to the Ukrainian coast: the fate of the missile cruiser Moskva, sunk by Ukrainian missiles last April, illustrated the dangers of doing this. And indeed the British intelligence update has it that the only Russian vessel so far to take up a blockade-like position, the corvette Sergey Kotov, is patrolling well to the south.

So grain ships could leave Odesa and hug the coast going south, where they would remain within the territorial waters of Romania, Bulgaria and Turkey. Russian interference with them there would be an act of war, against Nato member nations. Blockade runners used to do this in the Gulf in the old days, evading UN sanctions against Iraq by staying in Iranian territorial waters. It’s inconvenient, though, greatly lengthening travel times, and big cargo vessels don’t like following a twisting track close in to the coast.

So some grain would always get through by sea, and a fair bit could move by rail overland, though rail generally costs more than shipping and is limited in capacity. Insurance premiums would go up, too, probably by enough to deter most big shipping firms altogether. The blockade would not be total, but it would severely restrict supplies and drive up costs.

Would this be bad news for the Ukrainians?

Not really. They would lose some foreign-currency revenues, but that would hardly be their biggest issue. The Ukrainian economy has been shattered anyway: it is on a complete war footing, with military spending at 34 per cent of nominal GDP and government debt on a runaway upward trajectory. If the Ukrainians are overrun, they obviously won’t care about some lost grain revenues. If they defeat the Russians the West would simply have to stump up a slightly larger reconstruction loan afterwards.

But the possible Russian blockade would not really be aimed at the Ukrainians: it would be aimed at everybody else in the world. For a lot of people in Africa, rising grain prices could mean hunger or even starvation. There would be knock-on effects: not only grain based foods would be affected, as the price of livestock feed would rise. Food would get even more expensive in Britain than it already is. China’s new and rapidly developing appetite for meat and dairy would be more expensive to satisfy.

Vladimir Putin, ordering such a blockade, would hope to weaken Western support for Ukraine and turn Africa and China into firmer allies: it would have little direct effect on Ukraine itself.

So what could be done?

One option, already suggested, is convoys. Warships from willing nations – who would be Nato members – could escort groups of merchantmen from the Bosporus to Ukrainian waters, guaranteeing their right of passage on the high seas. Any Russian attack on these warships would again be an act of war, a first attack on Nato. Such convoy systems have been used at times to get tankers through the Strait of Hormuz in and out of the Gulf, defeating Iranian attempts to cut off the flow of oil. Indeed such a system may soon be going into effect in those waters, as Iranian attacks on shipping have been ramping up again lately. The ayatollahs are probably going to need another lesson.

Putin cannot make a first attack on Nato, as this would allow the US-led Nato armed forces to retaliate without being guilty of any escalation – and that would mean swift defeat in the Ukraine war. So convoys could be a reasonable solution.

But it might make more sense to deal with the problem another way. At the moment the Ukrainians are mounting a bloody counteroffensive into some of deepest and strongest defensive lines the world has ever seen, along the front lines from Zaporizhzhia to Donetsk. This is an extremely difficult mission. The tank enthusiasts of the Western armies, who confidently predicted that modern armour would win the war in Ukraine, would acknowledge that even Heinz Guderian needed to go around the Maginot Line rather than through it.

The Ukrainians punched through Russian lines last year because someone told them where all the Russian HQs were, and they had just received the Guided Multiple Launch Rocket System, fired mostly from the Himars vehicle. The GMLRS had enough range, was accurate enough and was available in enough numbers to pummel those HQs and knock them out.

But the Russians learned. Their HQs handling the fight today are much further back, and heavily defended. The Ukrainians have some Storm Shadow missiles from Britain, and some SCALPs (same weapon, different name) from France – but clearly these are not changing the picture as GMLRS did, though targets are being hit. The Storm Shadow has never had a particularly good reputation, and is subsonic, so relatively easy to shoot down.

Rather than setting up convoys and getting into a potential naval clash in the Black Sea, it might be simpler to just let the Ukrainians have the Army Tactical Missile System, the big brother of GMLRS. They’ve been asking for it time out of mind. It can go on the Himars, rather than needing a jerry-rigged ex Soviet fighter to fire it from, and it has a bit more range than Storm Shadow. More importantly it is known to work properly, and it travels at speeds in excess of Mach 3, so it is difficult to shoot down.

Russia would have to pull its HQs back well into the Sea of Azov to be safe from ATACMS. The whole land bridge and all of Crimea would be under Kyiv’s guns. The troops fighting and dying in the counter-offensive would have a serious chance to win: and the naval base of Sevastopol could and would be neutralised, so making any Russian grain blockade much more difficult to implement even if the Ukrainians’ drive to the Azov still didn’t succeed.

And sending the ATACMS is very arguably less escalatory than sending a Nato fleet into the Black Sea: indeed it’s barely more escalatory than sending the Storm Shadow already has been. Russia’s attempt to starve the world provides an excellent excuse for action.

It’s getting very hard to understand what Joe Biden thinks he’s waiting for.

Lewis Page is a former Royal Navy officer