Not wishing to start WW3, I take Ordinary bitter to mean abv up to 4.1% ...
Best bitter from 4.2% to 4.7% ...
Premium bitter from 4.8%
Why is 3.7% bitter, best bitter?

Some light reading on the subject https://en.wikipedia.org/wiki/Bitter_(beer) https://www.winning-homebrew.com/Best-Bitter.html Whilst looking this up on the all seeing Google eye, an advert popped up for Co Op best bitter at 2.8%. I would let the Grandkids have that with their school pack up. (just kidding Social services)

Some light reading on the subject https://en.wikipedia.org/wiki/Bitter_(beer) https://www.winning-homebrew.com/Best-Bitter.html Whilst looking this up on the all seeing Google eye, an advert popped up for Co Op best bitter at 2.8%. I would let the Grandkids have that with their school pack up. (just kidding Social services)

Looks like the boundaries change or people make mistakes (me included) ... the 'light reading' offered above has best bitter from 3.8% but that still wouldn't cover this one ... perhaps it's simply my bad.

Well folk march to the bar and say a pint of your best bitter landlord.
Thinking it means your finest ...
Only a few know roughly what best bitter is.

I deduce from the guff above (not your post) that best bitter is open to translation. And with most thing concerning the palate it may come down to ones own preference (taste) I always thought that a pale ale was just that and not a bitter. But most traditional pale ales would have matched the bitter description. If you stick to the best bitter tag my personal favourite would be the redefined Barnsley BB brewed really well by Acorn and by Stancill.

... and only 3.8% ...

The Acorn version is much improved at the Little Plough these days

There as been a trend in recent times to lower abv to lower tax paid on said ale.
And yet not lower the price to the consumer.
Some like Carling (lager granted) even labelled their abv as at least 0.2% higher than it actually was.
And they even said that that is what their customers preferred, in their defence.
I thought fraud was fraud.
Anyway the point I am trying to make is that apart from smaller brewers that like to brew strong ales and charge accordingly, the larger brewers have shifted what may have been best bitters into the (ordinary) bitter bracket.
A case in point being John Smiths.
And yet call it a premium beer.
Nonsense!!

Never been a John Smiths fan, his Nephew's ales on the other hand, different class IMO. Anyway where is Richard, he loves a pint of Smooth.

I am with you on that one ... Sam Smith's ales are superior.
I thought the were originally brothers ...

Quote: Stand-Offish "I am with you on that one ... Sam Smith's ales are superior. I thought the were originally brothers ...'" So did I but this suggests not. ( If I have read it correctly) https://www.gracesguide.co.uk/John_Smith%27s

Quote: Stand-Offish "I am with you on that one ... Sam Smith's ales are superior. I thought the were originally brothers ...'" So did I but this suggests not. ( If I have read it correctly) https://www.gracesguide.co.uk/John_Smith%27s

It says they were brothers ..John, Samuel and William.

In 1879 John Smith died and did not see the completion of this magnificent £130,000 building which opened in 1883. He left his personal estate, which included such items as the barrels and brewery equipment, in equal shares to his brothers, Samuel, a tanner from Leeds, and William, a bachelor.

A Tanner is just about a pint of SAM SMITHS is worth.

And as for the flat cask stuff 3d would be too much.

A pint of SMOOTH is the future.