Immigration/Passport Control; Google is not being very helpful today.

I know before Brexit you only had to pass through Customs/Immigration control in one EU country and then you were good to go across all of them but since Brexit I was wondering if that had changed concerning the U.K.?

Specifically my wife and I are in the early planning stages of a trip to London for our 25th anniversary and we were considering taking the Eurostar to Paris for a day trip(leave in the morning, return in the evening). We both are U.S. Citizens with U.S. Passports. Would we have to go through immigration control when entering France(Paris) and then again when we return that night when re-entering the U.K(London)?

It doesn't really matter if we do have to but I kind of wanted to get a sense of the travel time involved and possible delays involved in taking the Eurostar to Paris for a day trip.

Thanks In advance for any help.

While the UK is/was part of the European Union, they did not sign the Schengen agreement and you have always needed specific authorization (or acceptance) to enter the UK. When you get on the train in Paris there are UK immigration agents at the Paris train station who check passports/visas before you get on the train. This is not the case when you take the train to Brussels, which did sign the Schengen agreement, or almost any other European Country.

https://www.schengenvisainfo.c...visa-countries-list/

Holders of US passports, in general, do not need visas for either the UK or Europe, so there is no real inconvenience when taking the train. It is done at boarding, but most people arrive at the train station 30 minutes before departure (or whatever the ticket says for registration) and there is no customs/immigration process arriving at destination. The security checks are the same as taking an airplane, and rightly so.

Thank you so much, that is the information I was looking for.