It's true, but the alliance was before that...all began in 1294, and the Treaty of Windsor was sign in 1373 . Is the Oldest Alliance still in force. You can check over where:
That was the first battle with English help ( against Spanish and French ), but for several times we had English help , including in the Napoleonic Wars.
That is how the UK got involved in the Napoleonic wars, to help gaurantee Portuguese sovereignty against the naughty French and Spaniards. It was a tough old fight but Wellington helped see off the French and thus began the long road to France.
Remember, we might not have had Sharpe or Paddy if we didn't have the Anglo-Portuguese Alliance!