Scientists and art historians are trying to work out to what extent Leonardo had a hand in both versions of Virgin of the Rocks – the one in the Louvre, in Paris, and the replica in the National Gallery in London.

Doubts have long been cast over whether the Renaissance master made the London painting. Until 2010, the National Gallery believed it was mainly the work of assistants but, after restoring it, declared it possible that Leonardo painted all of the picture himself. Now, analysis of the vegetation and geology in the landscape around the central figures is reviving the debate.