Huh. I thought that the submission system automatically redirected you if there was a recent post with the same URL.

"bbc.co.uk" vs "bbc.com" in this case.

I've often thought about standardizing on one of those (probably bbc.com) and then rewriting the other URLs. But we don't have any reason to believe that would always work, or that it would continue to work in the future.

It wouldn't. Some BBC websites are .com-only (BBC Reel for example), others are .co.uk-only (BBC iPlayer). But it would work for BBC News, which I imagine is the majority of BBC links on HN. UK users would be redirected to the .co.uk url.

Or would it be possible to change the duplicate algorithm to simply understand bbc.com == bbc.co.uk?

That last bit is a good idea. I'm embarrassed not to have thought of it, or at least to have forgotten if we did.

Ah... three little characters. I checked several times and didn't notice the difference. An obvious thing to double check for the BBC in hindsight.

Only if it's recent. After a certain amount of time, the software will allow reposts.

Well, that's what I was questioning since the other submission was only 16 hours ago (sure counts as recent in my book!). In this case it turns out that the URLs were not actually identical as pointed out by a sibling comment.