A work from of Francis Bacon’s most famous series of paintings, of seated and often screaming popes, is to go on sale with an estimated value of £25m to £35m. When the canvas last went under the hammer in 2005, “Study for a Pope I” (1961) fetched £10 million — at the time this was a record for the artist. But even if the work goes under the hammer for the lower end of the latest price estimate, it would still equate to a rise in value of 150 percent.