THE TRANSATLANTIC MAGAZINE
The US Embassy in London has confirmed that they are now able to process adult US Passport renewal applications, as long as you are eligible to send your application by mail.
US Passports can be renewed at any time before or after they expire but services in recent months have been disrupted by the Covid-19 pandemic. However, because US Passports are only valid for entry to the US before their expiration date, if yours has expired during the lockdown and you plan to return to the US, the mail-in service will allow you to apply for a renewal.
The full details for eligibility, and where to send a renewal application, can be found on the US Embassy website, at https://uk.usembassy.gov/u-s-citizen-services/u-s-passports/renew-an-adult-passport/
If you are looking to apply for your first US Passport as an adult, the Embassy is not able to provide this service as first passport applications are not eligible for mail-in applications and in-person appointments are not currently available. The same applies if you are applying for a child's first US Passport or a Consular Report of Birth Abroad (CRBA), as these require in-person appointments.
If you need an urgent renewal for a child's or adult's US Passport, the Embassy ask that you do not submit applications by mail, but instead follow the instructions on this web page - https://uk.usembassy.gov/information-for-american-citizens-following-the-coronavirus-covid-19-outbreak/, as you may need an emergency passport.
For full information and regular updates, go to https://uk.usembassy.gov/u-s-citizen-services/security-and-travel-information/