The story focuses on Asterix and Obelix travelling to Roman-occupied Britain to help deliver a barrel of magic potion to a rebel Briton village, only to encounter obstacles that hinder their journey.

Mykingdomforanos, the village's chief, knwoing they will need help, assigns his best warrior, Anticlimax, to seek help from his cousin in Gaul, after he mentions how they rely on a potion of superhuman strength to resist the Romans.

Britannicus, learning they were heading for the city, guesses their likely actions and has all barrels of beer and wine confiscated fromm every tavern and inn, leading to the magic potion being seized amongst them.

Asterix and Anticlimax attempt to search for the thief with little luck, before finding the Romans had razed Dipsomaniax's tavern to the ground in their absence, arresting him and Obelix, per Britannicus' orders.

Learning they were imprisoned in the Tower of Londinium, they attempt to rescue them, though fortunately Obelix, recovering from a hangover, breaks himself and Dipsomaniax from prison, reuniting with Asterix and Anticlimax.

[4] As with stories involving encounters with various foreign people, Asterix in Britain makes fun of common English stereotypes,[5] though in the original publication both Rene Goscinny and Albert Uderzo included a foreword stating that this was done with no intention of insulting France's "famous rivals".