The Security Service reduced the threat level to Great Britain from Northern Ireland-related terrorism from substantial to moderate. This means that a terrorist attack is possible, but not likely.
In a written statement to Parliament, the Home Secretary Amber Rudd said:
Despite the change which has been made today, there remains a real and serious threat against the United Kingdom from terrorism and I would ask the public to remain vigilant and to report any suspicious activity to the police regardless of the threat level.
The decision to change this threat level is taken by the Security Service independently of ministers and is based on the very latest intelligence, considering factors such as capability, intent and timescale. Threat levels are kept under constant review.
The threat level to the UK from international terrorism remains at SEVERE, and the threat level to Northern Ireland from Northern Ireland-related terrorism also remains at SEVERE, meaning that an attack is highly likely.
Threat levels are designed to give a broad indication of the likelihood of a terrorist attack. They are a tool for security practitioners working across different sectors and the police to use in determining what protective security response may be required.
They also keep the public informed and give context to the protective security measures encountered every day.
There is more information about terrorism threat levels in the UK on the MI5 website.