This 35mm screening is part of the Big Screen Classic season at BFI Southbank and is also being shown (in NFT1) on February 25th. Details here.
Chicago Reader review:
Sergio Leone, famous for his spaghetti westerns shot in Spain, dared to invade John Ford's own Monument Valley for this 1969 epic. He brought back a masterpiece, a film that expands his baroque, cartoonish style into genuine grandeur, weaving dozens of thematic variations and narrative arabesques around a classical western foundation myth. It's very much a foreigner's film, drawing its elements not from historical reality but from the mythic base made universal by the movies. Moments of intense realism flow into passages of operatic extravagance; lowbrow burlesque exists side by side with the expression of the most refined shades of feeling. The film failed commercially and was savagely recut by its distributor, Paramount Pictures; copies from the European version may be as close as we'll ever get to the original. With Henry Fonda, Charles Bronson, Claudia Cardinale, and Jason Robards; Bernardo Bertolucci contributed to the script.
Here (and above) is the trailer.