What do I have to prove to be entitled to immigrate to Israel, if I have now discovered that my father ,with whom I re-established contact recently, is Jewish, and lives in Israel? He is not registered on my birth certificate but is willing to co-operate.I live in Europe.

You  have to prove a parent-child connection between both of you through genetic testing ordered by the family court in Israel. You should make a joint application together to perform D.N.A. testing, and if the results are positive, then the court will grant a declaration of paternity,which will provide the proof needed in order to be eligible to immigrate to Israel under the Law of Return.

In 2016 our law office successfully represented a Ukrainian non-Jewish woman in genetic testing proceedings before Petach Tikva Family Court which resulted in a declaration of paternity, which in turn provided the missing link, on the road to status and citizenship in Israel.