Although presented as an English dish, blackberry roll, by that name, seems to originate in the USA, possibly with the The Ann Arbor Cook Book of 1904.
Original Receipt from J.SalmonBlackberry Roll
A baked fruit roll containing apples and blackberries spiced with cinnamon
8oz blackberries
1 medium cooking apple (peeled, cored and finely diced)
3oz raisins
6oz white sugar
1 teaspoon ground cinnamon
1 teaspoon lemon juice
knob of butter
2oz flaked almonds
8oz shortcrust pastry
2 tablespoons cold water
glaze (beaten egg or milk)
Place the fruit, cinnamon, lemon juice, water and the butter into a saucepan and simmer gently, stirring regularly. The mixture should thicken until it is of marmalade (or thick jam) consistency. Cool the mixture then add the almonds. Pre heat the oven to 400F. Roll out the pastry (on a lightly floured surface) forming a rectangle (which will be rolled). Brush this very lightly with the glazing agent. Allow to dry then spread the fruit mixture evenly over the pastry. However, leave approx.½ inch from the edges of the pastry. Roll the pastry up like a Swiss roll. Seal the edges with water and glaze the outside of the roll. Place on a baking tray (greased baking sheet is better) and bake for 25-30 minutes until golden. Allow to cool slightly and serve with custard or cream.