There is a high threat from terrorism. Attacks could be indiscriminate, including on public transport and transport hubs and in places frequented by foreigners. Following an incident on a Thalys train in France on 23 August, there are increased security and ID checks at Belgian train stations.
Brussels hosts a number of international institutions (EU and NATO) and government and foreign embassy buildings which are sensitive locations.
There is considered to be a heightened threat of terrorist attack globally against UK interests and British nationals, from groups or individuals motivated by the conflict in Iraq and Syria. You should be vigilant at this time.