Boil the unopened tin of Condensed milk in enough water to completely cover the tin, for 1 hour.
Do not pierce the tin.
The Condensed milk will have solidified and turned into caramel
Leave the unopened tin of, what was, Condensed milk on the side until it is completely cold
Beat the Double cream until thick
Place the thick Double cream into a bowl
Open the cold tin of Condensed milk and mix the contents into the bowl of double cream
Crush up the 3 flakes, into small pieces, and add to the bowl
Crush the 3 digestive biscuits and sprinkle on top of the mixture