Do I have to register my passport online before going abroad?

If you hold a valid UK passport you are free to travel to any Schengen nation. (that's the EU loosely).

Beyond that you may need a visa.

There is no need to do anything online in relation to a passport.

Who is telling you this?

The passport office used to be based in Liverpool. So you need to give them a tel call (phone directory) a.s.a.p. to find out where they are based, and ask can your question be achieved. As it could take a few weeks for your passport to be renewed, maybe it would be just a well for you to take it personally, and then you can be sure that everything is in order prior to you leaving the country, and avoid any messy delay. Be prepared however, to spend most of the day there, as there may be quite a few people with the same idea, so take some sandwiches and a flask !! Caramac x

No you do not register a passport. Your passport is valid until the expiration date .You may need to get a Travel visa if your traveling to a country that requires one upon entry. Otherwise your fine.

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API applies to all airlines, it's an extra security measure which has been adopted by most countries before they will allow entry.

See all the info you need in the link.