The Schengen area, covering most EU countries, will be introducing the Entry/Exit System although now delayed until 2025 and also the ETIAS travel authorisation later in 2025. These will affect all British nationals (other than double nationals and those with EU residency) to undergo additional formalities when entering the Schengen area.
The UK has announced that it will introduce an Electronic Travel Authorisation for EU citizens from 2nd April. See the article in The Independent of 11th September. This will be similar to the Schengen area's ETIAS and will cost £10. At the moment, the ETA only applies to certain Middle Eastern countries. The extension to most other countries, including the EU, has now been announced for April 2025.
The ETA can be applied for from 5th March 2025 and will be required for travel into the UK from 2nd Aoril 2025. An ETA will be required for all non-British or Irish passport holders including babies and children.
Although this will not affect British citizens resident in the EU if they travel into the UK on their British passport, it will affect those EU-resident Britons who are double nationals but currently only use their EU passport and British citizens who have spouses or children who do not have British nationality or a British passport.
To find out more about how the ETA application will apply, go to the GOV.UK website.