I remember it vividly, because men would start slamming down liquor and beer around 9:30, and by 10:15 the streets would be full of angry drunken Glaswegians, a terrifying prospect. What was the point?
During the First World War the Central Control Board was established in 1915, which "effectively nationalised the brewery and pub industry in areas where the efficiency of munitions factories might have been damaged by drunkenness among workers" ( http://www.parliament.uk/business/publications/research/olympic-britain/leisure-and-lifestyles/liquor-up/ ). It should be noted that Lloyd George, who was Chancellor of the Exchequer, then Minister for Munitions and later Prime Minister, had a history of strongly campaigning in favour of temperance before he became Prime Minister, including for the failed 1908 Licencing Bill.
Some of those wartime measures were adopted as permament in the 1921 Licensing Act, which in Scotland limited weekday opening hours to 10pm. This wasn't relaxed until the 1976 Licensing (Scotland) Act ( http://www.legislation.gov.uk/ukpga/1976/66/part/V ). There has been further reform of this within the past 20 years.
http://www.academia.edu/1610660/Alcohol_licensing_in_Scotland_a_historical_overview is an excellent paper on the subject by James Nicholls.