Relationship dossier
Portugal
United Kingdom
Relationship assessment
A longstanding alliance and active partnership, sustained by defence cooperation and the Treaty of Windsor.
Portugal toward United Kingdom
+45Portugal has sustained cooperation with the United Kingdom through the Treaty of Windsor and shared NATO commitments, including defence and diplomatic coordination. The partnership spans successive governments and remains a significant element of Portugal’s relations with the UK.
United Kingdom toward Portugal
+45The United Kingdom has maintained the Treaty of Windsor alliance with Portugal and cooperates with it through NATO and bilateral defence and diplomatic engagement. Brexit changed the framework for UK-EU relations, while the bilateral partnership continued.
Overall relationship
+50The relationship rests on a longstanding treaty alliance and sustained cooperation in defence and diplomacy, reinforced by shared NATO membership. The two governments also maintain substantial economic ties. Brexit created new complications in the wider European framework, but the enduring bilateral alliance remains cooperative.
How to read these scores
Scores are rough judgments, not objective measurements or current verification. Directional scores describe government policy and conduct, not public opinion. The overall score is an independent estimate, never an average.
- −100
- Extreme sustained hostility
- −50
- Substantially adversarial
- 0
- Mixed or neutral, supported by knowledge
- +50
- Substantially cooperative
- +100
- Exceptionally close sustained partnership
“Not assessed” means there is no recorded score. Pair existence makes no claim about diplomatic recognition or established relations.
Relationship context
Overview
Portugal and the United Kingdom maintain a longstanding alliance, with substantial cooperation in defence, diplomacy and trade. Both are NATO allies, and the 1373 Treaty of Windsor remains a foundation for bilateral cooperation. The United Kingdom’s departure from the European Union introduced new practical issues, but did not displace the broader partnership.
Key developments
The Treaty of Windsor formalized the longstanding alliance between Portugal and the United Kingdom.
Portugal and the United Kingdom joined NATO as founding members, establishing a durable framework for allied defence cooperation.
The United Kingdom left the European Union, changing the wider framework governing its relations with Portugal.
Major uncertainties
- The extent and implementation of bilateral cooperation under post-Brexit arrangements continue to evolve.
- The practical scope of defence and security cooperation varies across policy areas.