Whilst 1 million to 1.25 million Europeans were captured and enslaved in Barbary slave trade, only a fairly small proportion of them were British. Plus the Arab states and Turkey don't really have much money to compensate us sufficiently.
I think compensation for the Norman conquest would be reasonable though. That caused apocalyptic losses in the UK - up to 50% of some regions being killed - and huge changes in power and land ownership too, which continue to the current day.
https://www.telegraph.co.uk/gift/869c791845927c87
France is almost as broke as the UK though, so I'm not sure we'll get much compensation from them. Although maybe if they got compensation for the Barbary slave trade too, they could pass some of that to us?
Buuutt.... The Norwegian Wealth fund is a good target! The Normans came to France from Norway, Sweden and Denmark just 200 years before 1066 - so even though they had intermarried with the French a bit in the meantime, perhaps we can make a claim on Norway for the Norman conquest?
Norwegian viking men also kidnapped large numbers of British woman to settle Iceland. Approximately 60% to 62% of Iceland's mitochondrial DNA (which traces matrilineal ancestry) originates from the British Isles, whereas 75% to 80% of the Icelandic Y chromosomes came from Scandinavia.
Iceland is pretty rich itself: perhaps we could get compensation from both Iceland and Norway?
That seems like a pretty good way to solve our economic problems...
Oh, and whilst they might have less loot available to hand over at present, there's certainly a moral case for compensation from the African and Carribean countries to the UK, for our pioneering role abolishing slavery - at huge cost to ourselves and loss of British lives. We can keep it on account... the way our economy is going,we're going to need it.
https://www.telegraph.co.uk/gift/3efe09f641830868