Anyone who has read New Grub Street will know that the difficulties of making a living writing books have been around for a long time. Some writers are blessed with private incomes, rich spouses or a love of asceticism that leaves them unhindered in the pursuit of the literary life. Others rely on a tenured post in academia, with its encouragement to spend extensive periods in well-stocked libraries, archives and manuscript stores, to supplement meagre earnings from scholarship. Many writers of non-fiction have to fit in literary work with a day job, such as journalism or broadcasting or (in the manner of T S Eliot) working in an office. It limits the time one can spend in archives, and if one wishes to write books using original material – and it is always pleasing if one can – that imposes a serious restraint. I have the good fortune to be able to spend one day a week in archives researching my next book, but I am still squeezed for time. Others are less fortunate: researching a book means forgoing the annual holiday or going part-time and never hoping to recoup lost earnings.

Technology, however, has helped in many ways. Most obviously there is the internet, allowing access to primary sources that used only to be available in libraries, during the restrictive hours in which libraries operate. Many letters are digitised