You can enter the UK with either a valid passport or a national identity card issued by a EEA country. It must be valid for the whole of your stay.
I am fully aware that this question was asked a number of times, for example here. However, since "Brexit" situation might have changed. Moreover, recently while travelling from Copenhagen airport to Dublin I was asked to prove validity of my identity card using additional document (e.g. driving license).
since "Brexit" situation might have changedWhere did you read this or got this information from ?