Loosened Regex on GB postcodes

The space is casually ignored by customers. It doesn't really matter, and won't cause any delivery / billing issues.
Other option is formatting the postcode input to contain the space. (The second part after the potential whitespace is always [0-9]{1}[a-zA-Z]{2})

Author: Gabor Peter Suranyi

app/code/Magento/Directory/etc/zip_codes.xml

@@ -455,12 +455,12 @@
     </zip>
     <zip countryCode="GB">
         <codes>
-            <code id="pattern_1" active="true" example="AB12 3CD">^[a-zA-Z]{2}[0-9]{2}\s[0-9]{1}[a-zA-Z]{2}$</code>
-            <code id="pattern_2" active="true" example="A1B 2CD">^[a-zA-Z]{1}[0-9]{1}[a-zA-Z]{1}\s[0-9]{1}[a-zA-Z]{2}$</code>
-            <code id="pattern_3" active="true" example="AB1 2CD">^[a-zA-Z]{2}[0-9]{1}\s[0-9]{1}[a-zA-Z]{2}$</code>
-            <code id="pattern_4" active="true" example="AB1C 2DF">^[a-zA-Z]{2}[0-9]{1}[a-zA-Z]{1}\s[0-9]{1}[a-zA-Z]{2}$</code>
-            <code id="pattern_5" active="true" example="A12 3BC">^[a-zA-Z]{1}[0-9]{2}\s[0-9]{1}[a-zA-Z]{2}$</code>
-            <code id="pattern_6" active="true" example="A1 2BC">^[a-zA-Z]{1}[0-9]{1}\s[0-9]{1}[a-zA-Z]{2}$</code>
+            <code id="pattern_1" active="true" example="AB12 3CD">^[a-zA-Z]{2}[0-9]{2}\s?[0-9]{1}[a-zA-Z]{2}$</code>
+            <code id="pattern_2" active="true" example="A1B 2CD">^[a-zA-Z]{1}[0-9]{1}[a-zA-Z]{1}\s?[0-9]{1}[a-zA-Z]{2}$</code>
+            <code id="pattern_3" active="true" example="AB1 2CD">^[a-zA-Z]{2}[0-9]{1}\s?[0-9]{1}[a-zA-Z]{2}$</code>
+            <code id="pattern_4" active="true" example="AB1C 2DF">^[a-zA-Z]{2}[0-9]{1}[a-zA-Z]{1}\s?[0-9]{1}[a-zA-Z]{2}$</code>
+            <code id="pattern_5" active="true" example="A12 3BC">^[a-zA-Z]{1}[0-9]{2}\s?[0-9]{1}[a-zA-Z]{2}$</code>
+            <code id="pattern_6" active="true" example="A1 2BC">^[a-zA-Z]{1}[0-9]{1}\s?[0-9]{1}[a-zA-Z]{2}$</code>
         </codes>
     </zip>
     <zip countryCode="US">