From 1 October 2021, an ID card will no longer allow you to enter the UK. You will need to present your international passport.
Brexit has been a fact since 1 February 2020. Since that date, the United Kingdom is no longer part of the European Union, which has consequences for the formalities to be completed if you wish to go there.
When the United Kingdom left the Union, transitional measures were put in place, in particular with regard to the documents required to enter British territory. It was agreed that European citizens could continue to move freely there until 30 September 2021 with their usual travel documents (i.e. the identity card for Belgians).
Today, these transitional measures expire. As of 1 October 2021, your identity card will therefore no longer be sufficient. You will need to show your international passport if you are travelling within the UK.
For a short stay, a visa will not be necessary, but as the UK is out of the Union, if you want to travel there for more than six months you will need to apply for a visa.
Also important: as the European Health Insurance Card is no longer valid in the United Kingdom either, the Belgian authorities recommend taking a travel assistance insurance before going there.
Source: Test Aankoop/Test Achat