Sara Wheeler explains why every week for several decades - despite knowing nothing about art - she has called in to London’s National Gallery to look at the same two paintings.

'This habit of mine,' writes Sara, 'started by accident when I moved to London forty years ago' when she first set eyes on Botticelli's 'Portrait of a Young Man' and van Eyck's 'Portrait of a Man.'

'I have come to realise,' says Sara, the extraordinary power of 'familiarity, close contact and regular attention'.

Producer: Adele Armstrong
Sound: Peter Bosher
Production coordinator: Gemma Ashman
Editor: Richard Fenton-Smith