In a medium size saucepan place condensed milk, brown sugar, glucose syrup, golden syrup and butter. Over a low heat, cook until the sugar has dissolved and the mixture is glossy. This will take around 10 minutes, make sure you stir the mixture continuously.
Increase the heat slightly to medium/low. Bring the mixture to a simmer. Cook for 6-8 minutes, continuously stirring. The mixture will thicken and start to come away from the base of the pan. Note, the longer you cook it the harder your fudge will be.
Remove from the heat and stir through white chocolate until it melts and combines with the caramel mixture. Mix through your walnuts.
Place mixture in your lined pan and spread it out evenly. Use the back of a spoon to smooth.
Cover with plastic wrap and refrigerate until firm.