Marriage Trends in the UK

 The dataset Vital statistics in the UK: births, deaths and marriages at https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationestimates/datasets/vitalstatisticspopulationandhealthreferencetables shows interesting trends for England and Wales, Scotland and Northern Ireland from 1887 to 2017. There are no marriage statistics for England and Wales for 2018 and later.

For opposite-sex marriages, the chart below shows annual deviation from the long-term mean as a percentage.

The trends in all three jurisdictions are similar.

There's an increase to about 1970, likely reflecting the increase in population. After marriage becomes less popular.

There's a minor increase in marriages at the start of the First World War and a much larger increase after the war.

For the Second World War, the opposite is the case.

The peak in marriages around 1970 is due to the marriage of baby boomers. In 1971 in England and Wales the most frequent age for marriage was 20 - 24 years. By 1994 it had shifted to 25-29 years and by 2015 30 - 34 years.

Religious marriage ceremonies reached a peak in popularity in 1919 in England and Wales. By 1992 the number of couples choosing civil marriage ceremonies overtook those opting for religious ones. The number of civil ceremony marriages has remained reasonably stable since the 1970s while the decline in marriages has been in religious ceremonies. Church marriage records are to be less likely a useful source for genealogists researching this period.