diff --git a/backend/app/agents/brand_agent.py b/backend/app/agents/brand_agent.py
index efba634..75c9703 100755
--- a/backend/app/agents/brand_agent.py
+++ b/backend/app/agents/brand_agent.py
@@ -146,6 +146,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Each bullet should be one actionable sentence
 - Start with the issue, then the recommendation
 - Example: "Logo placement incorrect (bottom-left) - move to top-right corner per guidelines"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included
diff --git a/backend/app/agents/channel_best_practices_agent.py b/backend/app/agents/channel_best_practices_agent.py
index 811cfd6..98bbd1f 100644
--- a/backend/app/agents/channel_best_practices_agent.py
+++ b/backend/app/agents/channel_best_practices_agent.py
@@ -139,6 +139,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Each bullet should be one actionable sentence
 - Start with the issue, then the recommendation
 - Example: "CTA placement below fold - move above fold for better visibility"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included
diff --git a/backend/app/agents/channel_tech_specs_agent.py b/backend/app/agents/channel_tech_specs_agent.py
index 7e6cb3e..67e630a 100644
--- a/backend/app/agents/channel_tech_specs_agent.py
+++ b/backend/app/agents/channel_tech_specs_agent.py
@@ -147,6 +147,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Each bullet should be one actionable sentence
 - Start with the issue, then the specification requirement
 - Example: "Image resolution 72dpi - increase to minimum 150dpi for print quality"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included
diff --git a/backend/app/agents/lead_agent.py b/backend/app/agents/lead_agent.py
index 1fb39ce..52ed9c5 100755
--- a/backend/app/agents/lead_agent.py
+++ b/backend/app/agents/lead_agent.py
@@ -147,6 +147,7 @@ Your summary should:
 - Each bullet: one sentence, actionable
 - Do NOT include page numbers, document names, or source citations. Keep all feedback self-contained and actionable.
 - For 'Passed': briefly note any amber items in 1-2 bullets
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 {revision_context}
 Here are the specialist reviews:
 {self._format_reviews(reviews)}
diff --git a/backend/app/agents/legal_agent.py b/backend/app/agents/legal_agent.py
index cc4ef54..babebde 100755
--- a/backend/app/agents/legal_agent.py
+++ b/backend/app/agents/legal_agent.py
@@ -149,6 +149,7 @@ If the proof is nonsensical, not a marketing material, or cannot be analyzed, se
 - Do NOT include page numbers, document names, or source citations (e.g., no "Page 10", "per the Legal Guidelines"). Feedback must be self-contained and actionable.
 - Start with the issue, then the requirement
 - Example: "Missing APR disclaimer - add representative APR per FCA requirements"
+- IMPORTANT: Use British English spelling throughout all output (e.g. "authorised" not "authorized", "colour" not "color", "capitalise" not "capitalize", "organised" not "organized", "centre" not "center", "analysed" not "analyzed").
 """
 
         # Determine if revision fields should be included