At present, travellers do not need to undertake any Covid-19 testing prior to travel or after arrival, nor do they need to complete any UK Passenger Tracing Forms prior to travel. Nor will it be necessary to observe a quarantine on arrival in the UK. There are specific conditions for direct and indirect flights from China.
All EU citizens wishing to enter the UK (including citizens making a stopover in the UK) must travel with a valid passport. The national identity card is no longer valid as a travel document for entry into the UK. Only those who have applied for the EU Settlement Scheme and have settled or pre-settled status, or are awaiting a decision on their application, will be able to continue to use their ID card until 31 December 2025: https://www.gov.uk/guidance/visiting-the-uk-after-brexit
More information on the use of the DNI to enter the UK can be found at the following link: https://www.gov.uk/uk-border-control/before-you-leave-for-the-uk