Parliament has been briefed on why the UK has raised its terrorism threat level after four people died in a terror attack in Vienna on Monday.
The independent-from-Government Joint Terrorism Analysis Centre says the threat level now stands at 'severe', which means an attack is believed to be highly likely.
The 20-year-old Vienna perpetrator, who was shot dead by police, was described as an Islamist terrorist.
Both France and the UK have adjusted their terror threat levels.
Security Minister James Brokenshire MP explained the reasons behind the change.
"I should stress that this change in the threat is a precautionary measure, and is not based on any specific threat," he said.
"However, there is a risk that the recent attacks in France and Austria could have a galvanising effect in other parts of Europe, including the UK, so the change of threat level is therefore seen as prudent."
Parliament was told that Tuesday's decision was based on the latest intelligence and was met with support from the opposition.
Shadow Security Minister Conor McGinn voiced his support.
"We wholeheartedly support the decision of the Joint Terrorism Analysis Centre, that the terror threat be raised from substantial to severe and we share the Government’s view that this decision should not cause undue alarm, but is a precautionary move and demonstrates the importance of us all remaining vigilant."
At this stage, the military has not yet been called to assist the civil authorities, but should the level rise again the UK will set Operation Temperer in motion.
After the Manchester Arena bombing in May 2017, Operation Temperer was enacted as the UK's terror threat level was raised to critical.
It was put into action a second time following the Parsons Green train bombing in September 2017.
Operation Temperer is designed to be a temporary measure and allows for up to 3,800 military personnel to be put on UK streets and to guard infrastructure sites like railway stations and Parliament.
This will in turn allow an increase in the number of armed officers on patrol in key locations.