It’s June, and the country-house summer opera festivals are now in full swing. Glyndebourne, which opened the season last month, has now been joined by its leading emulators — Garsington in Oxfordshire, The Grange in Hampshire and Longborough in Gloucestershire; and next month a newcomer, Winslow Hall Opera in Buckinghamshire, will be putting on La Traviata with much the same cast that shone last year in its greatly admired production of Lucia di Lammermoor.