Report any threats to national security - such as terrorism and espionage - to MI5 (also known as the Security Service).
Call 999 or the police anti-terrorist hotline on 0800 789 321 to report an immediate threat to life or property.
Your message will be sent over a secure Internet connection. You can choose to remain anonymous or include your contact details so the Security Service can get in touch with you.
All the information you send will be treated confidentially.
Other ways to contact MI5
You can report threats by phone or in writing.
Freephone: 0800 111 4645
Telephone: 020 7930 9000
From outside the UK: +44 (0)20 7930 9000
The Enquiries Desk
PO Box 3255
Further information on reporting suspicious activity to MI5 can be found on GOV.UK's website.