diff --git a/README.md b/README.md
index 3cd89b6..b80bd61 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 Adds fields to the tender object to describe the legal basis of the contracting process – that is, the laws and regulations that govern the contracting process and that grant legal authority to the procuring entity.
 
-The `tender.legalBasis` field is a `Classification` object. Example classification schemes are [LEX](https://en.wikipedia.org/wiki/Lex_(URN)), [CELEX](https://eur-lex.europa.eu/content/help/faq/intro.html#help8) and [ELI](https://en.wikipedia.org/wiki/European_Legislation_Identifier).
+The `tender.legalBasis` object identifies the legal basis of the contracting process and, optionally, the law or regulation from which the legal basis was derived. Each law or regulation is identified by an `id` drawn from an identifier `scheme`. Example identifier schemes include [LEX](https://en.wikipedia.org/wiki/Lex_(URN)), [CELEX](https://eur-lex.europa.eu/content/help/faq/intro.html#help8) and [ELI](https://en.wikipedia.org/wiki/European_Legislation_Identifier).
 
 To identify the procedure used, whether by formal name or by legal citation, use the [`tender.procurementMethodDetails`](https://standard.open-contracting.org/latest/en/schema/reference/#release-schema.json,/definitions/Tender,procurementMethodDetails) field.
 
@@ -18,13 +18,20 @@ In the European Union, this extension's fields correspond to [eForms BT-01 (Proc
 
 ## Example
 
+The legal basis for a contracting process is the Public Contracts Regulations 2015, which is the [transposition](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=LEGISSUM:transposition) into UK law of EU Directive 2014/24.
+
 ```json
 {
   "tender": {
-    "crossBorderLaw": "Italian procurement legislation",
+    "crossBorderLaw": "UK procurement legislation",
     "legalBasis": {
-      "id": "32014L0025",
-      "scheme": "CELEX"
+      "id": "https://www.legislation.gov.uk/id/uksi/2015/102",
+      "scheme": "ELI",
+      "wasDerivedFrom": {
+        "id": "32014L0024",
+        "scheme": "CELEX",
+        "uri": "https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32011R1007"
+      }
     }
   }
 }
@@ -36,9 +43,14 @@ Report issues for this extension in the [ocds-extensions repository](https://git
 
 ## Changelog
 
+### 2024-11-28
+
+* Add `tender.legalBasis.wasDerivedFrom` field.
+* Add `legislationClassificationScheme.csv` codelist.
+
 ### 2023-08-01
 
-* Add 'ELI' to `+itemClassificationScheme.csv`.
+* Add 'ELI' to "+itemClassificationScheme.csv".
 
 ### 2021-01-19
 
diff --git a/codelists/+itemClassificationScheme.csv b/codelists/legislationClassificationScheme.csv
similarity index 100%
rename from codelists/+itemClassificationScheme.csv
rename to codelists/legislationClassificationScheme.csv
diff --git a/extension.json b/extension.json
index b603965..51bb0ed 100644
--- a/extension.json
+++ b/extension.json
@@ -15,7 +15,7 @@
     "release-schema.json"
   ],
   "codelists": [
-    "+itemClassificationScheme.csv"
+    "legislationClassificationScheme.csv"
   ],
   "contactPoint": {
     "name": "Open Contracting Partnership",
diff --git a/release-schema.json b/release-schema.json
index 4fcd619..8aec8ac 100644
--- a/release-schema.json
+++ b/release-schema.json
@@ -13,10 +13,102 @@
         },
         "legalBasis": {
           "title": "Legal basis",
-          "description": "The legal basis of the procedure.",
-          "$ref": "#/definitions/Classification"
+          "description": "The law or regulation that governs the contracting process and grants legal authority to the buyer or procuring entity.",
+          "type": "object",
+          "properties": {
+            "scheme": {
+              "title": "Scheme",
+              "description": "The identifier scheme from which the legislation's identifier is taken.",
+              "type": [
+                "string",
+                "null"
+              ],
+              "codelist": "legislationClassificationScheme.csv",
+              "openCodelist": true,
+              "minLength": 1
+            },
+            "id": {
+              "title": "ID",
+              "description": "The legislation's identifier taken from the scheme.",
+              "type": [
+                "string",
+                "null"
+              ],
+              "minLength": 1
+            },
+            "description": {
+              "title": "Description",
+              "description": "A textual description or title for the legislation's identifier.",
+              "type": [
+                "string",
+                "null"
+              ],
+              "minLength": 1
+            },
+            "uri": {
+              "title": "URI",
+              "description": "A URI to uniquely identify the legislation.",
+              "type": [
+                "string",
+                "null"
+              ],
+              "format": "uri"
+            },
+            "wasDerivedFrom": {
+              "title": "Was derived from",
+              "description": "The law or regulation that the legislation transposes, updates or builds upon. For example, in the EU, national legislation transposes EU directives.",
+              "$ref": "#/definitions/Legislation"
+            }
+          },
+          "minProperties": 1
         }
       }
+    },
+    "Legislation": {
+      "title": "Legislation",
+      "description": "A law or regulation.",
+      "type": "object",
+      "properties": {
+        "scheme": {
+          "title": "Scheme",
+          "description": "The identifier scheme from which the legislation's identifier is taken.",
+          "type": [
+            "string",
+            "null"
+          ],
+          "codelist": "legislationClassificationScheme.csv",
+          "openCodelist": true,
+          "minLength": 1
+        },
+        "id": {
+          "title": "ID",
+          "description": "The legislation's identifier taken from the scheme.",
+          "type": [
+            "string",
+            "null"
+          ],
+          "minLength": 1
+        },
+        "description": {
+          "title": "Description",
+          "description": "A textual description or title for the legislation's identifier.",
+          "type": [
+            "string",
+            "null"
+          ],
+          "minLength": 1
+        },
+        "uri": {
+          "title": "URI",
+          "description": "A URI to uniquely identify the legislation.",
+          "type": [
+            "string",
+            "null"
+          ],
+          "format": "uri"
+        }
+      },
+      "minProperties": 1
     }
   }
 }