diff --git a/ATTRIBUTION.md b/ATTRIBUTION.md
index 7942228d6..66dcdfa4b 100644
--- a/ATTRIBUTION.md
+++ b/ATTRIBUTION.md
@@ -10,7 +10,7 @@ Generated-in-code art is original and has no file to list: the UI icon set (`cra
 |---|---|---|---|---|
 | `assets/hyphenation/en-us.pat` | DesignCraft contributors (generated) | trained from the Moby list by DesignCraft's patgen | Public Domain (CC0-1.0) | Our own Liang hyphenation patterns (no TeX patterns) |
 | `assets/hyphenation/en-us.dic` | Grady Ward (Moby Hyphenator II word list); converted by DesignCraft contributors | https://www.gutenberg.org/ebooks/3204 (file `mhyph.txt`, SHA-256 `eeb30474c86b8af3469035ec1a0913e35905325ca885290db9dfed9881e230ac`), via DesignCraft | Public Domain | ~165k words with break points; drives spelling and hyphenation |
-| `assets/spelling/en-extra.txt` | WordCraft contributors | original word list written for this repository (common modern words the Moby list lacks); no other dictionary copied | MIT OR Apache-2.0 | ~220 lowercase English base forms supplementing spelling (#520) |
+| `assets/spelling/en-extra.txt` | WordCraft contributors | original word list written for this repository (common modern words the Moby list lacks); no other dictionary copied | MIT OR Apache-2.0 | ~240 lowercase English base forms supplementing spelling (#520), including British spellings (#40) |
 | `assets/hyphenation/pl.pat` | Hanna Kołodziejska, Bogusław Jackowski, Marek Ryćko (Polish TeX hyphenation patterns, 1987–1995); hyph-utf8 package | https://github.com/hyphenation/tex-hyphen (`hyph-utf8/tex/generic/hyph-utf8/patterns/tex/hyph-pl.tex`, SHA-256 `83ddbbd21bc06a44bc4f4a4c49c38782e809cff5f026b764c044daa29e818843`), bundled unmodified | MIT (the file is offered under MIT or Knuth's public-domain terms; WordCraft uses MIT, whose notice is in the file's header) | 4,053 Liang patterns and 20 exception words; Polish hyphenation |
 | `assets/hyphenation/pt.pat` | Pedro J. de Rezende, J. Joao Dias Almeida, Leonardo Araujo, Aline Benevides (Portuguese TeX hyphenation patterns, 1987–2024); hyph-utf8 package | https://github.com/hyphenation/tex-hyphen (`hyph-utf8/tex/generic/hyph-utf8/patterns/tex/hyph-pt.tex`, SHA-256 `c110a39e501db372d1d755e1c64464321a2efa7d8e9617f66001000389b941f2`), bundled unmodified | BSD 3-clause (the file's licence header names it and carries the notice) | 426 Liang patterns and 2 exception words; Portuguese hyphenation |
 | `assets/hyphenation/it.pat` | Claudio Beccari (Italian TeX hyphenation patterns, 2008–2014); hyph-utf8 package | https://github.com/hyphenation/tex-hyphen (`hyph-utf8/tex/generic/hyph-utf8/patterns/tex/hyph-it.tex`, SHA-256 `6ce56ed6ed2ca7c0688838e366e6595e0429f984f4fc6e96ec045cebb1e76a47`), bundled unmodified | MIT (the file is offered under LPPL 1.3+ or MIT; WordCraft uses MIT, whose notice is in the file's header) | 355 Liang patterns, no exception words; Italian hyphenation |
diff --git a/assets/spelling/en-extra.txt b/assets/spelling/en-extra.txt
index 41567c7d7..7d04908e3 100644
--- a/assets/spelling/en-extra.txt
+++ b/assets/spelling/en-extra.txt
@@ -26,7 +26,12 @@ chatroom
 checkbox
 checklist
 childcare
+clamour
 clickable
+colourful
+colourisation
+colourise
+colourless
 configurable
 copyedit
 coronavirus
@@ -54,6 +59,7 @@ ecommerce
 email
 emoji
 emoticon
+endeavour
 esports
 facebook
 favicon
@@ -71,6 +77,7 @@ geolocation
 gigabit
 gigabyte
 github
+glamour
 globalization
 google
 groupthink
@@ -80,6 +87,9 @@ hashtag
 healthcare
 homepage
 homeschool
+honour
+honourable
+honourably
 hotspot
 hyperlink
 hypertext
@@ -106,6 +116,7 @@ logout
 lowercase
 makeover
 malware
+manoeuvrable
 megabyte
 megapixel
 meme
@@ -127,6 +138,7 @@ onboard
 online
 onscreen
 outsource
+paediatric
 paralegal
 passcode
 petabyte
@@ -139,10 +151,13 @@ podcast
 popup
 prequel
 printout
+prioritise
 prioritization
 prioritize
+privatise
 ransomware
 recyclable
+rigour
 ringtone
 roadmap
 rollout
@@ -171,6 +186,7 @@ subfolder
 sunscreen
 superfood
 superuser
+synthesise
 tagline
 takeout
 techie
@@ -188,6 +204,7 @@ touchpad
 touchscreen
 trackball
 trackpad
+travelogue
 upcycle
 upload
 uppercase
diff --git a/crates/proof/src/lib.rs b/crates/proof/src/lib.rs
index 671a0e803..6b34a4a5d 100644
--- a/crates/proof/src/lib.rs
+++ b/crates/proof/src/lib.rs
@@ -812,6 +812,43 @@ mod tests {
     }
 
     /// The supplement stays a sorted list of lowercase base forms.
+    /// #40: British spellings and their inflections are not flagged.
+    #[test]
+    fn british_spellings_are_known() {
+        for w in [
+            "judgement",
+            "defence",
+            "licence",
+            "programme",
+            "catalogue",
+            "behaviour",
+            "colour",
+            "colourful",
+            "colourless",
+            "honour",
+            "honoured",
+            "honouring",
+            "honours",
+            "honourable",
+            "rigour",
+            "glamour",
+            "clamour",
+            "endeavour",
+            "paediatric",
+            "prioritise",
+            "prioritised",
+            "prioritising",
+            "privatise",
+            "privatised",
+            "synthesise",
+            "travelogue",
+            "manoeuvrable",
+        ] {
+            assert!(is_correct(w), "{w}");
+        }
+        assert!(check_spelling("The programme honoured her rigour and prioritised colourful, paediatric care.").is_empty());
+    }
+
     #[test]
     fn supplement_is_sorted_lowercase() {
         let words: Vec<&str> = EXTRA_EN.lines().filter(|l| !l.is_empty() && !l.starts_with('#')).collect();