britain 's leading art gallery has uncovered new evidence in its attempt to keep a £ 1million constable masterpiece that was legitimately brought to britain .
the 1946 document bears the signature of a dealer called karola fabri and seeks permission for the transfer of artworks from budapest to zurich , including one by constable identified as fishing boat .
the discovery of the permit in the archives of budapest 's museum of fine arts is the latest twist in an increasingly fraught dispute between the tate and the descendants of the painting 's original owner , baron ferenc hatvany , who died in 1958 that