Q&A: Why is Portugal known as Britain’s oldest ally?

The first point to make is that Portugal is actually England's oldest ally. It is only because England is now part of the United Kingdom that Portugal is counted as a British ally. The friendship between England and Portugal goes back to 1147 when English crusaders helped King Alfonso I capture Lisbon from the Muslims. This led to an English colony in Lisbon and to frequent contacts between the nobles of the two kingdoms.

In 1386 Richard II of England agreed the Treaty of Windsor with John I of Portugal. English troops had recently helped John drive out a Spanish invasion and it was decided to turn the friendship into a formal alliance. The key section of the treaty reads: “If, in time to come, one of the kings or his heir shall need the support of the other, the ally shall be bound to give aid and succour to the other, to the extent required by the danger to his ally’s realms, lands, domains, and subjects.”