We've got as far as the strong Bitters. It's weird to see Double Diamond - for me the epitome of a shit, highly advertised, keg beer - lumped together with classy beers like Bass and White Shield. Just shows what a decade or two can do to a beer's image.
High-gravity bitters and pale ales are well hopped, have very good substance to the palate and clear appearance to the eye. They are the drinks of the moneyed customer and are important to the brewer, for they are favoured by folk who otherwise prefer spirits. They are usually the only beers on sale in American bars and cocktail bars of the more classy restaurants and hotels. At their head come the three national beers: Bass Pale Ale, Worthington India Pale Ale, and Ind, Coope and Allsopp's Double Diamond, which with Guinness Stout are to be found in most bars, even those of tied houses. Their draught equivalents are met less frequently, mostly in their own tied houses or in the big free houses or hotels owned by such groups as Trust Houses Ltd, Levy & Franks Ltd, j. Lyons & Co Ltd, and many others. Their gravity lies between 1047º and 1053º, approaching five per cent alcohol.
In competition with the national beers, many other breweries have introduced their own higher-gravity beers, pale ales with alcoholic strength resulting from gravities ranging from 1045º to well above 1057º. Some are slightly sweeter than the national beers. Intensive advertising campaigns are arranged to establish their names with the public, and extensive arrangements ensure their availability in many thousands of public houses and bars.
Another group of medium high-gravity pale ales are sold under the name of Export. As a rule they lie between the light ales and the national beers but sometimes are well up to the 1047º level. Finished with care and pasteurized, they have excellent storage qualities but may develop a distinctive, very slightly baked flavour. This is not unpleasant and makes these Export beers rather similar to the general run of Continental light beers."
"The Book Of Beer" by Andrew Campbell, 1956, pages 89-90.
This passage taught me something dead important. Something I'm embarrassed not to have already known.