Preheat the oven to 180°C/350°F/gas mark 4. Line two baking sheets with baking parchment.
Place the softened block butter, light brown soft sugar, caster sugar, milk and vanilla extract in a bowl. Beat with an electric mixer until light and fluffy.
Add the flour, baking powder, cinnamon, nutmeg, salt and oats and mix until well combined. Stir through the raisins.
Roll the dough into golf ball sized balls and place them well spaced apart on the baking sheets. You should get about 12-13 cookies. Flatten them very slightly with your hand. If the dough is too soft to roll, pop it in the fridge for half an hour or so to firm up.
Bake the cookies for about 12-15 minutes, until they are golden around the edges. Remove from the oven and immediately transfer them to a wire rack to cool.
The cookies are best on the day they are baked but will keep in an airtight container for 2-3 days.