Loosing? Learn the English language, people!

Neither is a true imperative, though, but I don't think that's the issue at hand, here.

It isn't a true imperative because the suggestive voice of 'why don't you?' doesn't permit a full imperative. It's an attempt to be direct while being indirect. Nonetheless, its justification depends on the second person being addressed.

Be honest!
Do be honest!
Why don't you be honest?

The auxiliary verb is a strengthener, which is a function that becomes confused with the other normal use of 'to do' as soon as you switch to the third person. The copula doesn't take an auxiliary verb except for this strengthening function.

Looking at the very limited data above, it's to do with how dynamic the action of "to be" is.

That's certainly a way of looking at it, in view of parallel constructions ('why doesn't she take out the rubbish?') but I don't think it's the crucial issue. I'm sure that some people understand 'to be honest' as very dynamic, but grammatically it is a simple attributive construction.

A lot of native English speakers would have no problem with "why doesn’t she be honest with the British people..." It didn't raise any problems with me on first reading.

Arguably, this is precisely the general problem that keeps this thread alive. :)

"Why isn't she honest with the British people..." has a subtly different meaning here.

Which is? I don't think there's any difference in meaning at all.

However (and this may be related to how you think of a difference in meaning) I've also just worked out (I think) where this comes from. It must come out of parliamentary language, in which speakers don't address one another directly; the speaker here was an MP. I could imagine they're quite used to modifying second-person constructions in this way.

Which is? I don't think there's any difference in meaning at all.

This is the crux of the matter. You're barking up the wrong tree with parliamentary language and imperatives. "Why doesn't she be honest with the British people..." implies to me (in the context) that she'd have to take a specific future action (saying how she plans to retain it). "Why isn't she honest with the British people..." implies that she's been habitually dishonest.

This is why linguists test data on native speakers. You're trying to come up with grammatical reasons why the phrase is wrong, when the experimental data doesn't bear this out.

I agree with the tense change implied in the two different phrasing. But for a more specific tense change would "why won't she be honest" be better?

^^This, there clearly is a difference between the two phrases. However I do think parliamentary language plays a part - a lot of the choice of phrasing in Parliament is unique because the speakers are challenging the person they're addressing to take the 'specific future action' right away.

For example, "why doesn't she be honest with the British people" specifically means "get up Theresa, and actually tell the truth now in response to my point."

Actually, doesn't that mean it is an imperative?

Again, as @fizzy.bleach says, doesn't that imply a future habit of being honest rather than a specific action of being honest?

Also the band Teleman are growing on me despite my initial dislike. Part of the reason I couldn't get to grips with them earlier was a grammatic quirk in their song Cristina:

Cristina's so good
She makes me go across town
*She makes me to lie down*

U wot m8?

In the opening song of their new album, there's this:

*I haven't got a place where to lay my hat*
I long for the five-star life like that

Is this poetic licence or just wrong? Is it acceptable? Why?

This is the crux of the matter. You're barking up the wrong tree with parliamentary language and imperatives. "Why doesn't she be honest with the British people..." implies to me (in the context) that she'd have to take a specific future action (saying how she plans to retain it). "Why isn't she honest with the British people..." implies that she's been habitually dishonest.

Er? '[...] so why isn’t she honest with the British people [in saying / and says (or some other way of replacing the infinitive dependent on 'doesn't')] how she plans to retain it' has exactly that meaning (of an implied future action). Yes, 'why isn't she honest with the British people ...' without the rest of the sentence can be seen to mean something different, so perhaps I shouldn't have left out the rest. 'Why doesn't she be' adds nothing except for a faint trace of the strengthening auxiliary verb but only jars (and is quite unnecessary).

This is why linguists test data on native speakers. You're trying to come up with grammatical reasons why the phrase is wrong, when the experimental data doesn't bear this out.

Well, as above, I think you're wrong in postulating a potential for a different meaning here. I have every sympathy with attempts to introduce nuances of meaning that don't quite fit into 'established' grammar, by the way, as ultimately grammar is the servant of logic and not the other way around. However, here I think it's an attempt to export a construction from its established context in a way that doesn't work.

The question of parliamentary language or not is very interesting. It's obviously only speculation in this case, but there is, of course, a strong tendency in English to express things indirectly (e.g., ironically), partly because people had to tug their forelocks most of the time, but also because the grammatical opportunities are there and easily accessible, e.g. conditionality. By contrast, a lot of German native speakers can't do the German Konjunktiv properly, which is undoubtedly partly why it isn't used as much as equivalent forms of expression in English. I wonder to what extent, if any, parliamentary convention shaped general usage, if at all, or whether it's the other way around.

I agree with the tense change implied in the two different phrasing. But for a more specific tense change would "why won't she be honest" be better?

Yes, much better.

For example, "why doesn't she be honest with the British people" specifically means "get up Theresa, and actually tell the truth now in response to my point."

It may mean that, but as I said above (not having seen your post while typing), the same notion can be expressed with the same force in a non-clunky construction. mashton's variant is the best.

Is this poetic licence or just wrong? Is it acceptable? Why?

Probably syllable-filling because they couldn't get the lines to fit the music. :)

I suppose I'd better try to avoid listening to this band's work.

We can come up with more elegant ways of expressing the sentiment, but that doesn't prove that the original utterance is somehow incorrect. FWIW "why won't she be honest" also implies some habituality which also includes the past, for me. A repeated refusal to be honest, despite several opportunities.

I'd actually be interested to see what other people think about the acceptability of the original. I suspect it's less wrong and jarring than you think, Oliver, which begs the question (steady!!!) - why should we care that this person "broke the rules" and used that construction?

It works fine at communicating the intended meaning.

Agreed.

Can we get back to more meaningful errors?

Like apostrophe's being overused.

She makes me to lie down

U wot m8?

It's a sneaky Biblical reference - Psalm 23 (He makes me to lie down by the still waters). Note she's called 'Christ-ina'. Teleman means 'tell-a-man' i.e. they perform missionary work through their music.

I need a to lie down.

"Could of" and "should of" really gets me.

I've seen enough Vicar of Dibley to know that doesn't sound right. Isn't it 'maketh me to lie down in green pastures'?

That's KJV, I think.

Wearing a hijab in front of children! Thanks, Guradian.
The deputy leader of far-right group Britain First has been found guilty of religiously aggravated harassment after hurling abuse at a Muslim woman wearing a hijab in front of her four young children.

people using admittance instead of admission (confession). football pundits usually

Gotten makes me angry.

In front have her four young children.

Why do so many cunts refer to a toilet as a fucking bathroom? For example:
Royal Ascot 2015, Mrs American "Could you tell me where the nearest bathroom is?"
Constable S "You don't appear to need a bath, so I assume it is a toilet you require? If so it is directly behind you". It is pervading British English and I don't like it.
Also cunts that don't look before they ask for directions. (perhaps this is equally at home in I hate thread).

Shitter.

But the word toilet itself is a derivative of French and originally used in the context of dressing and washing oneself, so indeed bathroom or washroom are rather close companions.

I prefer "loo". They're all euphemistic anyway. Aside from shitter.

Bog