Preheat the oven to 350°F/180°C/Gas Mark 4 (the middle bottom right hand oven of a 4-door Aga, if you're that lucky).
Prepare the tin by applying a thin layer of margarine and lining with two layers of greaseproof paper.
Put the margarine, sugar, fruit, water, bicarbonate of soda and mixed spice in a saucepan over a moderate heat. Bring to boil and simmer for 1 minute.
Pour into a mixing bowl and allow to cool1.
Add eggs, flour and salt to cooled mixture. Mix well and pour into prepared tin.
Bake for about one and a quarter hours. You may need to put brown paper over the top if cake starts to singe before it is cooked throughout.
Cake is ready when an inserted skewer comes out clean - leave to cool on a wire rack.
SERVE!