diff --git a/agenda/gwr.py b/agenda/gwr.py
index 992c69f..9471866 100644
--- a/agenda/gwr.py
+++ b/agenda/gwr.py
@@ -7,6 +7,8 @@ from time import time
 
 import requests
 
+url = "https://www.gwr.com/your-tickets/choosing-your-ticket/advance-tickets"
+
 
 def extract_weekday_date(html: str) -> date | None:
     """Furthest date of GWR advance ticket booking."""
@@ -30,13 +32,12 @@ def extract_weekday_date(html: str) -> date | None:
 def advance_tickets_page_html(data_dir: str, ttl: int = 60 * 60 * 6) -> str:
     """Get advance-tickets web page HTML with cache."""
     filename = os.path.join(data_dir, "advance-tickets.html")
-    url = "https://www.gwr.com/your-tickets/choosing-your-ticket/advance-tickets"
     mtime = os.path.getmtime(filename) if os.path.exists(filename) else 0
     if (time() - mtime) < ttl:  # use cache
         return open(filename).read()
-    r = requests.get(url)
-    open(filename, "w").write(r.text)
-    return r.text
+    html = requests.get(url).text
+    open(filename, "w").write(html)
+    return html
 
 
 def advance_ticket_date(data_dir: str) -> date | None:
diff --git a/update_gwr_advance_ticket_date.py b/update_gwr_advance_ticket_date.py
new file mode 100755
index 0000000..6688754
--- /dev/null
+++ b/update_gwr_advance_ticket_date.py
@@ -0,0 +1,70 @@
+#!/usr/bin/python3
+"""Update GWR advance ticket date cache."""
+
+import configparser
+import os.path
+import smtplib
+from email.message import EmailMessage
+from email.utils import formatdate, make_msgid
+
+import requests
+
+from agenda import gwr
+
+SMTP_HOST = "4angle.com"
+EMAIL = "edward@4angle.com"
+NAME = "Edward Betts"
+
+
+def send_mail(subject: str, body: str) -> None:
+    """Send an e-mail."""
+    msg = EmailMessage()
+
+    msg["Subject"] = subject
+    msg["To"] = f"{NAME} <{EMAIL}>"
+    msg["From"] = f"{NAME} <{EMAIL}>"
+    msg["Date"] = formatdate()
+    msg["Message-ID"] = make_msgid()
+
+    msg.set_content(body)
+
+    s = smtplib.SMTP(SMTP_HOST)
+    s.sendmail(EMAIL, [EMAIL], msg.as_string())
+    s.quit()
+
+
+def get_data_dir() -> str:
+    """Read data dir from config."""
+    config_filename = os.path.join(os.path.dirname(__file__), "..", "config")
+
+    assert os.path.exists(config_filename)
+
+    config = configparser.ConfigParser()
+    config.read(config_filename)
+
+    return config.get("data", "dir")
+
+
+def main() -> None:
+    """Get date from web page and compare with existing."""
+    filename = os.path.join(get_data_dir(), "advance-tickets.html")
+    existing_html = open(filename).read()
+    existing_date = gwr.extract_weekday_date(existing_html)
+
+    new_html = requests.get(gwr.url).text
+    open(filename, "w").write(new_html)
+
+    new_date = gwr.extract_weekday_date(new_html)
+
+    if existing_date == new_date:
+        return
+
+    subject = "New GWR advance ticket booking date: {new_date}"
+    body = """Old date: {old_date}
+New date: {new_date}
+
+{gwr.url}
+
+Agenda: https://edwardbetts.com/agenda/
+"""
+    send_mail(subject, body)