A passport may seem like a simple travel document, but at a foreign border it also represents the credibility of the state that issued it. Immigration authorities assess not only the individual traveller, but also the reliability of the country’s identity records, document security, migration management and willingness to accept responsibility when citizens violate immigration rules.

The European Commission is to grant Turkey conditional approval this Wednesday for visa-free travel within the EU's Schengen area, sources have told the BBC.