Preheat the oven to 200°C (180°C fan/Gas Mark 6).
Pat the hens dry with kitchen paper and, if you like, tie their legs together with kitchen string.
In a small bowl, mix the softened butter with salt and ground black pepper. Finely chop the rosemary and thyme leaves, then stir them into the butter.
Gently loosen the skin over the breast and thigh of each hen. Spread half of the herb butter under the skin, then rub the rest all over the outside.
Stuff the cavity of each hen with half a lemon, two lightly crushed garlic cloves and a sprig each of rosemary and thyme.
If you like, drizzle a little olive oil into a roasting tin, then place the hens on a roasting rack or directly in the tin.
Roast at 200°C (180°C fan/Gas Mark 6) for 20 minutes, then reduce the heat to 190°C (170°C fan/Gas Mark 5) and roast for a further 30–40 minutes, until a meat thermometer inserted into the thickest part of a thigh reads 75°C.
Remove the hens from the oven and leave them to rest for 5–10 minutes before serving.