Passports and other documents are being lost because the Government requires them to be posted when applying for a first adult UK passport or the first UK passport after becoming a British citizen. Additionally some applicants for a UK immigration status have to post their identity document.
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Those affected spend time and money getting replacements, even if temporary, and may be unable to travel or prove their rights e.g. to rent or work in the meantime and may be at risk of identity theft. Checking services have been provided before. The Nationality Document Return Service and Joint Citizenship and Passport Service were introduced in 2016 then withdrawn when applications went online in 2018/19. The successor UKVCAS service does not include passport applications.