A while ago I treated you to a dissertation entitled “Does The Sun Set On The British Empire?”, and concluded that it doesn’t. The UK’s widely scattered overseas territories, sparse though they are, mean that the sun is still always shining, somewhere in the world, over British territory.

The most important territories in maintaining this late-empire sunlight are the Pitcairn Islands, in the Pacific, and the British Indian Ocean Territory, in the Indian Ocean. To illustrate that, I offered the sunlight chart below, showing how Pitcairn and BIOT catch the sunlight when it’s dark in the UK.

In fact, as my map at the head of this post shows, BIOT is pivotal. There, I’ve plotted the distribution of light and darkness, across the globe, at 02:15 Greenwich Mean Time, during the June solstice of 2024.*

And here’s the situation at the December solstice:

Just after the sun sets in Pitcairn, it’s dark over every British territory except BIOT.

I’m revisiting the situation because the UK government has announced plans to hand over sovereignty of the Chagos Archipelago, which houses BIOT, to Mauritius. The announcement was made in October 2024, but the original agreement has now been contested by a new government in Mauritius. And the situation is further complicated by the fact that BIOT houses a large US military base on the island of Diego Garcia, so the new Trump administration also has a say in the process. (Meanwhile, the unfortunate Chagossians, evicted from their homeland in 1968 to make way for the military base, have so far been given no voice in the negotiations.)

The current proposal suggests that the military base would be maintained under a long-term lease agreement, in which case British sovereignty would be lost, and BIOT would cease to exist. At that point, the role of easternmost British territory would fall to the Sovereign Base Areas (SBAs), in Cyprus.

The SBAs are worth a few paragraphs, both because they’re relatively obscure, and because their existence, as sovereign military territories, perhaps has some slight relevance to how the situation on Diego Garcia might play out, should the Trump administration raise strong objections to the current plan.

The SBAs came into existence when Cyprus gained its independence from the UK in 1960. Under the Treaty of Establishment, the UK retained sovereignty over about 250 square kilometres of the island, in two separate areas—the Western Sovereign Base Area of Akrotiri, and the Eastern Sovereign Base Area of Dhekelia. These have extremely complicated boundaries, designed to avoid Cypriot settlements while including British military establishments. The Eastern SBA contains three Cypriot enclaves—the towns of Ormideia and Xylotymbou, and the area surrounding the Dhekelia power station (which is crossed by a British road). It also features a long northward extension along the road to the village of Ayios Nikolaos, which now houses a signals intelligence unit.

And the whole border situation became even more complicated after the Turkish invasion of Cyprus in 1974, which has left the island traversed by a UN buffer zone. British territory, including the Ayios Nikolaos road, forms part of the buffer zone. Elsewhere, the Turkish-controlled town of Kokkina has its very own buffer zone. Here’s an overview map, followed by some detail of the SBAs:

(Interestingly, the British military settlements within the SBAs are referred to as cantonments, a military term which, to me at least, has something of a colonial ring to it, given its association with British rule in India.)

The relevance, here, to the current situation of Diego Garcia, is because the UK government made plans to hand the SBAs back to Cyprus in 1974, but were persuaded to retain sovereignty by the USA, which valued access to signals intelligence in the Eastern Mediterranean, as well as a convenient location from which to fly, among other things, U2 spy planes. The difference, of course, is that the Cypriot government appears to have been compliant with that arrangement, whereas it seems unlikely, at time of writing, that the Mauritians would agree to such a deal.

We’ll see how it goes. Meanwhile, I’ve plotted another sunrise/sunset graph, showing how sunlight is handed off between the two key players in the absence of BIOT:

(For my sunlight calculation, I’ve plugged in the latitude and longitude of the easternmost part of the Eastern SBA—Ayios Nikolaos.)

It’s close—in June there’s less than an hour when it’s dark in both Pitcairn and the SBAs. But, if BIOT goes, when the sun sets on Pitcairn, it will also set on (what’s left of) the British Empire.

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* I haven’t plotted British Antarctic Territory, because territorial claims in Antarctica are in abeyance under the Antarctic Treaty.