In 1930 John, the eldest of the Mertons' five sons, brought home the drawing prize from Eton and this proved a turning point in both his and his father's lives. It awoke in Merton some latent interest and he spent months in Italy with his son seeing all the great collections of Renaissance paintings. He began to make a remarkable collection of pictures of the period 1450–1520. From 1944 until his death he was a member of the scientific advisory board of the National Gallery, and its chairman from 1957 to 1965. He was also a trustee of the gallery, and of the National Portrait Gallery from 1955 to 1962. Merton was knighted in 1944 and in 1956 was appointed KBE due to his achievements as a treasurer of the Royal Academy. He was awarded the Holweck Prize in 1951 and the Rumford medal of the Royal Society in 1958.