I remember sitting in my grandparents’ parlour in Bilston, Wolverhampton, watching him tell jokes on New Faces in the 1970s. It’s where he got his first TV break.

Great Britain has come a long way since. Sir Lenny has come a long way too. He also appeared on The Black and White Minstrel Show, something he later said he was contractually obliged to do, and deeply regrets. I think we all regret that show.

Today he’s a national treasure. But like so many celebrities, he fancies being a political force as well.

So he’s co-written a new book, The Big Payback, calling for Britain to pay slavery reparations.

The idea, he tells us with his best straight face, is serious. All black Britons “personally deserve money for the effects of slavery”.

Sir Lenny believes this vast redistribution of wealth can “dismantle the foundations” of Western society built on slavery and racism, and “rid the world of racism”.

It would be a brilliant joke if it actually was a joke. It we take it as seriously he does, we’ll regret it even more than The Black and White Minstrel Show.

Slavery was one of history’s great crimes. Historians estimate that up to four million Africans died as a direct result of the trade between 1500 and 1900.

British ships carried around 2.6 million of the 12 million enslaved Africans taken to the Americas. Surprisingly, just 5% went to North America, with more than half ending up in Brazil.

Sir Lenny believes it’s time to settle the bill. He writes that “the reason we have racism today” is because of the transatlantic slave trade.

But there are plenty of problems with the notion of reparations.

No Briton alive today held or trafficked slaves, yet would still have to pay. Also, the trade also involved Portugese and Spanish colonialists, Arab traders and African chiefs, who I doubt will stump up.

And if we start demanding reparations for historical crimes, where do we stop? Every nation on earth could make a case. By that logic, Britain should be sending invoices to descendants of the Romans, Vikings, Spanish, Germans and French.

And if we do pay, can we claim a discount for the fortune we spent dispatching the Royal Navy to suppress the global slave trade from 1807?

I’ll leave that debate to the historians. Or TV comedians. I’m a financial journalist, so let’s focus on the money.

Western powers owe $100trillion in reparations to Caribbean countries, according to the Brattle Group. Britain’s share would be around £18trillion. Given our annual GDP of £3trillion, we could go for it and clear the entire debt in just six years.

But only if we didn’t spend a single penny on anything else in that time, including the NHS, schools, roads, defence, police, pensions, benefits, tax, food and water.

We really would have “dismantled the foundations” of Western society, though not quite in the way Sir Lenny imagines.

I doubt it would “rid the world of racism” either. Britain would be crawling with racists if this went through.

And I don’t think Britain’s 2.4million black citizens will be that thrilled either, as they’d be living in a lawless, bankrupt hellhole, with a heap of cash.

Divided up among our population of 69 million, Sir Lenny’s plan would cost every man, woman and child £260,870 each. If we listened to our national treasure, we wouldn’t have any treasure left.

It’s the worst idea since The Black and White Minstrel Show. Happily, we haven’t signed up to this so we’re not contractually obliged to do it. And we won’t.

I still like Lenny Henry. Just not to the tune of £18trillion.