According to recent research, we British prefer beer that is nearly half as strong as those on the Continent. The average strength of our favourite beers is apparently 4.4%, as opposed to the 7.9% European drinkers prefer. I'm not very surprised: most of us know that the British brewing tradition is radically different from most of those that can be found in Europe. This is not just a matter of brewing techniques.
The First World War brought serious restrictions on pubs and brewing; at one point it was illegal to buy a round. I've read an account of how a man wanted to buy drinks for himself and his wife and was refused because that constituted a round; his wife had to go to the bar to buy her own. Under the Defence of the Realm Act, licensing hours were introduced, beer was watered down and an extra penny tax put on a pint. The Temperance movement was quite a force in the UK and the brewing industry was not immune to what was, at that time, its increasing impact; these laws gave them a significant boost, although a Temperance appeal to the monarch to declare that a toast to the king could be made just as loyally with a non-alcoholic drink was given short shrift by the Palace. The Temperance movement eventually lost most of its influence when Prohibition was ended in the USA, but the effects of First World War legislation on beer, including upon its strength, continued long after the war ended. In particular, the precedent of gradually but continually cutting beer strengths continued until the 1970s when CAMRA published the strength of all beers: brewers who didn't voluntarily reveal the strength, or weakness, of their products were angry and dismayed when the Campaign had their products analysed and published the sometimes embarrassing results.
Beer drinking was was strongly identified with industrial labour. Workers wanted to slake their thirst after a day's work, especially those in heavy industry: cool pints that didn't have you sliding under the table after just a few were preferred, hence the former popularity of mild in the old industrial heartlands. The decline in mild drinking must be partly due to the ending of much of our industrial base. (There's also another possible factor that I wrote about in May.)
Traditionally, we Britons used to spend long evenings in the pub, often meeting early in the evening and staying until closing time: such long evenings demand a beer that can be drunk in fairly large quantities. Additionally, formerly popular pub games such as darts, dominoes and bar billiards required the players not to be legless.
Our beer strengths have recovered to some extent since CAMRA's exposure of the scandal of weak beer sold at premium prices. It used to be said that one national brand could have been sold legally during the American Prohibition, and there were frequent rumours that some brewers put chemicals in beer to give you a slight headache so that the next day you thought you had a hangover. I've no idea how true these stories were, but the fact that they circulated shows how some drinkers viewed the beers they were sold with a certain amount of distrust.
All these factors are specific to the UK, and have shaped our preference for beers that are less strong than those on the Continent. Personally, I'd prefer to have more pints in the 4.0% to 5.0% range than fewer at 7.9%, but that's what I've grown up with and what I've become used to. I don't think I'm untypical in this respect. The research was by academics at Anglia Ruskin University based on 65,000 reviews on the app Pint Please.