I am intrigued by your posting. What is the source for this spelling?

Google does not have anyone with this spelling of a surname. The closest I can find on the BMD indexes worldwide is Jancerevicius in Illinois

Could it be Jozef JANKOVIČ the Czechoslovakian artist b 1937 - then 18-19 years old and studying at Bratislava. Someone may know if he visited UK briefly. There is an exhibition of his work in London.

Best of luck with this one.

Howard