The announcement that Titian's Diana and Callisto has been acquired for the nation is a cause for huge celebration. Not just the fact that a masterpiece will not be going abroad - but also for what it shows about our cultural institutions. Many people thought I was wrong to make boosting philanthropy the mainstay of arts policy. But in difficult times I thought it was right to focus my energies on helping to stabilise the finances of the country's cultural fabric - which I passionately believe is one of our greatest assets.