In a small bowl, stir together the digestive biscuit crumbs and 100g sugar. Add the melted butter and mix well. Press into the bottom of a 23cm loose bottomed cake tin. Cover the outside of the pan with a few layers of foil to make it waterproof.
In a large bowl, cream together the cream cheese and 200g sugar until soft and smooth. Stir in the lemon juice and vanilla. Scrape the bottom of the bowl occasionally with a spatula to prevent lumps. Beat in the eggs one at a time, then fold in the bits of Daim(R) bar. Pour the mixture into the prepared cake tin. Place this tin into a larger cake tin or a roasting tin with at least 2.5cm tall sides. Put into the oven, then fill the larger pan with water, creating a water bath.
Bake for 90 minutes in the preheated oven, checking after 45 minutes to refill the water bath. After 90 minutes, turn off the oven and leave the cake inside for about an hour. Chill at least 4 hours before removing from pan.