I don't know if you can call football the national game, however according to Wikipedia, it is the most popular in the UK as follows.
Like many team sports, football is organised on a separate basis for each of the countries of the United Kingdom and each has its own Football Association, national team and league system, though a few clubs play outside their country's respective systems for a variety of historical and logistical reasons. Football was developed in the UK and is comfortably the most popular sport.
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