Wales, Scotland and the island Ireland have a combined population of 14.6 million whilst England has a population of 53 million. Are there any historical reasons for this huge difference. All of Ireland, Wales and Scotland is habitable. It's not like comparing the population of Alaska with New York.
In 1811, the population of England and Wales (they were not counted separately in these censuses) was 10.2m, The population of Scotland was 1.8m and the population of Ireland was 7.8m.
http://homepage.ntlworld.com/hitch/gendocs/pop.html
So, at that time, the combined population of Ireland, Scotland and Wales was probably equal to or greater than that of England. (bearing in mind, that the very high population of Ireland in the early 19th century was an anomaly. As recently as 1750, the population of Ireland had been only 2.6m. The introduction of the potato as a staple crop had enabled an explosion of the Irish population (though most were very poor subsistence potato croppers) which only lasted 100 years before a fungal disease attacked the potatoes, causing the potato famine, and an Irish population decline from which Ireland has still not recovered. (The combined population of the Republic of Ireland and Northern Ireland today is 6.4m.))
By 1931, the population of England and Wales had grown to 40m, (400%), the population of Scotland had grown to 4.8m (270%), and the population of Ireland had shrunk to 4.2m (-46%).
The causes were:
Greater growth of industrialization and cities in England.
The potato famine (which resulted in 1m deaths) in Ireland, and then decades of emigration from Ireland (much of which to England).
In short, when all the countries were agricultural, England had the most land and the richest land, so had the most population, but the combined population of Ireland, Scotland, Wales was briefly (in the early 1800s, propelled by the fragile potato economy in Ireland) about the same as that of England .
Once industrialization and the growth of cities set in (primarily in England), the population migrated to and multiplied in the cities. This caused the population of urban England to grow faster than the populations of less urban Scotland and Ireland (some of which was due to emigration to England from Scotland and Ireland).
The potato famine in Ireland, in the 1840s also contributed to a decline in the Irish population, and an Irish diaspora, which encouraged emigration for a further century.