Preheat the oven to gas 4/180C/fan oven 160C. Lightly grease a 18cm (7in) square tin.
Place the dates in a small pan with 2 tbsp water, bring to the boil and simmer for 3-4 mins until soft. Add more water if needed to create a stiff paste. Set aside.
Place the lemon juice, low calorie sweetener, golden syrup and margarine in a large pan and heat gently until melted. Add the remaining ingredients including the date paste and mix well. Press the mixture into the tin, smoothing the surface and bake for 20-25 mins until set and golden.
Remove from the oven, cut into 8 bars and leave to cool in the tin. Store in an airtight container for up to 3 days.