Christmas pudding - how long to cook?

I've got my nana's recipe for Christmas pudding (which in essence is a heavy fruit cake.

However, I don't know how long to cook it in a double boiler.

I remember that the uncooked pudding was covered with wax paper and tied with string then left to boil in a double boiler. (Later on is was turned out, a bit of brandy was poured over it and it was lit.)

Can anyone advise me how long I should cook the pudding for, more or less-ish.

Here are the ingredients to give you an idea of the possible size of the pudding:
¼ lb raisins
¼ lb sultanas
¾ lb currants
¼ lb mixed peel
¼ lb beef suet (skinned & chopped)
¼ lb brown sugar
2 cups self raising flour
2 eggs
2 cup breadcrumbs
1 oz shelled almonds
2 tsp mixed spice
Chopped prunes/dates (optional)
Grated carrot
Rind & juice 1 lemon
1 cup brandy

But cooking time in a double boiler?

Your thoughts are appreciated.