How long will double cream stay whipped

There are two levels to this question. If you are using modern whipping cream as a starting point, then the trick for a longer lasting whipped cream is stabilization. If this is some farm bought milk you are skimming the cream from, then you have the additional problem that your cream is not fatty enough. Modern creams are concentrated with a centrifuge.

To get good whipped cream, whip it cold until it doubles in volume and you get firm peaks. Stabilize the whipped cream by hanging it in a cheese cloth in the refrigerator or by adding gelatin.To use the gelatin, dissolve 2 teaspoons of unflavored gelatin into 2 tablespoons of cold water. Work out the lumps. After the gelatin expands, mix in a quarter cup of cream and heat the mixture to dissolve the gelatin.  Cool over ice and mix a bit. Complete 2 cups of cream and proceed as you would to finish your whipped cream.

The brands that used to work may have changed their formulation in response to carageenan shortages. If they use less emulsifier, a lower quality product, or different emulsifiers such as guar gum, locust bean, or xanthan gum, the stability of the whipped cream may suffer. If the cream you can get isn't stable enough, you can add unflavored gelatin to stabilize it. Method is in 'Joy of Cooking', or here.

May2013: Looks like carrageenan is still on the USDA organic list Shortage has eased, but whipping problems could still be due to variations in quality of supply.