Why do UK publishers use apostrophes instead of speech marks?

[FibonacciEddie]

I'm kind of with @Ursa major. I use " for spoken/conversations between characters, but ' for when they quote or emphasize another character. I get confused with italicized words in quotes. To me, an italicized words means a thought.

"Jill told me it is the 'best coffee' she has ever had."

"Jill told me it is the best coffee she has ever had."

Although, the more works by UK authors I read, the more I'm getting used to seeing,
'Jill told me it is the best coffee she has ever had.'

But with social custom to double finger an emphasize statement in day-to-day life, one would think writing it like this would make more since,

'Jill told me it is the "best coffee" she has ever had.'
It is easier to type too.

somehow (whatever the rights and wrongs of convention) ... this sentence just makes me itch
'Jill told me it is the "best coffee" she has ever had.'

But I also agree that italicized words means an internal direct thought.

so... we're left with no right answer

 

[Ursa major]

'Jill told me it is the "best coffee" she has ever had.'

Could it perhaps be that what is making you itch is not only the use of two types of quotation mark but also the mixing up of the tenses and the unnecessary** use of quotation marks in the middle of a sentence of dialogue?

Surely it should either be:

'Jill told me it was the best coffee she had ever had.'

or (and I don't really like this, as it seems unnecessarily fussy):

'Jill told me, "It's the best coffee I've ever had."'

** - I'm assuming that the quotation marks around the words, best coffee, are not meant to be signifying that it was far from being the best coffee Jill had ever had... but if they are, the (fictional) listener wouldn't be able to see those marks, so something outside the dialogue -- such as "air quoting" or a facial expression -- would have to be mentioned for it to make sense.

 

[Wayne Mack]

somehow (whatever the rights and wrongs of convention) ... this sentence just makes me itch
'Jill told me it is the "best coffee" she has ever had.'

But I also agree that italicized words means an internal direct thought.

so... we're left with no right answer

I would choose to only highlight the word best and then either quotes or italicization would work.

'Jill told me it is the "best" coffee she has ever had.'
'Jill told me it is the best coffee she has ever had.'

Strange thought, but after typing the choice in, I feel that I have a slightly interpretation of the two phrases. In the quoted version, the best seems mocking, indicating the coffee was bad. In the italicized version, I feel that best was emphasized, indicating the coffee was quite good. Anyone else feel this way?

 

[Venusian Broon]

I would choose to only highlight the word best and then either quotes or italicization would work.

'Jill told me it is the "best" coffee she has ever had.'
'Jill told me it is the best coffee she has ever had.'

Strange thought, but after typing the choice in, I feel that I have a slightly interpretation of the two phrases. In the quoted version, the best seems mocking, indicating the coffee was bad. In the italicized version, I feel that best was emphasized, indicating the coffee was quite good. Anyone else feel this way?

Yes the use of quotation marks as scare quotes is widespread!, and is exactly how I would interpret your first example.

I'm not sure I would use italics though. Best is best, Adding an additional accent seems overkill. Now, if she was speaking,

"This is the  best!"

Then this makes more sense as you are telling us something about her vocal delivery and character.

 

[Vertigo]

For me it depends on how it is said. If the speaker is emphasising the 'best' then italics if not then no italics. If they're being sarcastic then the quotes. For me the quotes and italics convey totally different sentiments.