Line an 8x8-inch tin with baking paper, leaving a little bit hanging over the edges for easy removal later.
Melt the chocolate and condensed milk together. You can do this over low heat on the stove, in a double boiler, or in short bursts in the microwave in a heatproof bowl. The mixture should be thick and glossy.
Remove from the heat and quickly stir in half of the Crunchie bar pieces. Transfer the fudge mixture to your lined tin and press it evenly into place.
Add the rest of the Crunchie pieces on top of the fudge and gently press them down to help them stick.
Refrigerate your Crunchie fudge for 1-2 hours until firm, then cut into squares and enjoy.