Can "unless" be used in unreal past (with would have)?

Question

I found conflicting information about the subject: BBC World Service states that:

And we cannot use unless with would to talk about unreal future situations:

• If he didn't take everything so seriously, he would be much easier to work with.

• If he weren't so bad-tempered, I would help him to get the work done.

We cannot use unless with would have to talk about unreal situations in the past either:

• If you hadn't driven so recklessly, you wouldn't have had this accident.

• If you hadn't had that last glass of wine, this would never have happened.

While Education first website shows usage in all conditionals. What is correct then?

Why I cannot find anything about this usage besides that BBC website?

Answer 1

Here's another warning against usage of 'unless' for impossible conditions:

https://dictionary.cambridge.org/us/grammar/british-grammar/conditionals-and-wishes/conditionals-other-expressions-unless-should-as-long-as

As for Education First vs BBC, the former is Sweden-based (according to Wikipedia). Not sure if the usage of 'unless' differs in AE though.

Answer 2

Unless X = if not X.

You have to completely flip ALL negative ("nots") and affirmative expressions in X when converting from one to the other. This can be tricky.

If he did not take everything so seriously, he would be much easier to work with.

Unless he took everything so seriously, he would not be much easier to work with.