The popularity of Porter wasn't lost on provincial brewers. By the 19th century brewers in most of Britain were now brewing Porter. Though they were usually unable to match the large London breweries for quality.
There's one telling sentence in the text below: "Two or three of the principal London houses brew as much or more malt liquor than all the brewers of Scotland and Ireland put together." That's an indication of the different scale of brewing in London compared to the rest of the country. This would change in the second half of the 19th century when Bass and Guinness overtook the London brewers in terms of size.
But, notwithstanding, very good porter has been made in many provincial towns; and in Scotland and Ireland efforts have been made to establish porter breweries, which have more or less succeeded, according to the skill and capital employed. Dublin porter, although inferior to that made in London, has obtained a considerable celebrity; and the porter of Aberdeen is not considered behind it in quality. But all this is only comparative. Two or three of the principal London houses brew as much or more malt liquor than all the brewers of Scotland and Ireland put together.
In Scotland, the business of brewing porter has rather declined, in consequence of the increased demand for draught ale. In Glasgow, better porter is produced than at Edinburgh ; but their ale is generally considered inferior to that made at the latter city. There cannot be any doubt whatever, that in such a flourishing commercial district as Glasgow, the brewing of ale and porter might be carried to great perfection, were judicious steps previously taken, in selecting proper localities, for malting the finest samples of barley.
The brewers of London obtain their supplies of malt from Norfolk,—and other districts where fine barley is produced; for in England, wherever it is abundant, a malt-house is established.
The climate of the west coast is too humid for making fine barley into fine malt, and for keeping it any length of time ; but the drier climate of the Lothians is at hand, and were the brewers of Glasgow to establish maltings on the eastern coasts, they could supply themselves constantly with fresh made malt, the production from which might stand competition with the ales of Edinburgh or the porter of London. It has been urged, however, that their water is defective for the purposes of brewing. It may be so; but where a great commercial advantage is to be obtained, skill and capital overcome many difficulties.
The question has often been asked, Can porter be made on a small scale, to approach near in quality to that made in London ? The question cannot be easily decided. In many provincial towns, it is very useful to make two or three brewings of porter to take up hard ale, which answers excellently, when it has been properly treated with hops; and although the quality of such a production is not equal to porter made in London, it may be equal to the purpose for which it is intended. In many districts, during the summer months, this description of malt liquor, when mixed half-and-half with mild ale, forms a very refreshing beverage, and is in much demand where it can be produced."
"Brewing and Distillation" by Thomas Thomson and William Stewart, 1849, pages 275-277.
I'm a bit Portered out for the moment. Time to jump back to the 1950's again.