What evidence can I use to prove my CSI?
Some EU citizens may have had private medical insurance during the period they were self-sufficient or a student. This can be used as CSI.
There are also other ways to prove CSI. This depends on your country of citizenship and your arrangements. In some EU countries, students abroad were covered by specific national-level policies, whereas some students can still count on their parents’ insurance. An EHIC card issued by an EEA member state other than the UK can also be used. Form S1 (or its predecessor forms E109 or E121) and form S2 (or its predecessor form E112) and form S3 are also accepted. Form E104, however, is not mentioned in the Home Office’s guidance.
A useful resource about Forms E104 and S041 can be found here: https://blogs.kent.ac.uk/eu-rights-clinic/csi-form-e-014-s041/. This is a very complex area of law and those wishing to rely on it should consider getting legal advice.
Note: this question, like other FAQs on Comprehensive Sickness Insurance (CSI), relates to applications for British citizenship, when considering whether periods of past residence were lawful. the3million’s Young Europeans have published a very useful document on key Citizenship facts which you can find here: http://www.t3m.org.uk/t3m_YE_KeyCitizenshipFacts.