As of October 1, 2021, ID cards will no longer be sufficient to enter the United Kingdom. The island state insists on the presentation of the passport. This also applies expressly to EU citizens.
One of the reasons for the decision was that ID cards are supposed to be susceptible to forgery and no longer meet the security requirements. At the same time, there is a direct connection with the exit from the European Union.
The entry requirements will be relaxed with effect from October 4, 2021 at least for fully vaccinated people. In this article explains the rules for England. Those for Scotland, Northern Ireland and Wales may differ.