Place the agar powder and water in a small saucepan and whisk until the agar is dissolved. Then turn on to medium heat and bring to a simmer.
Meanwhile, blend all other ingredients well.
From this point, you'll need to work fairly quickly so the mix doesn't have time to separate. Have your glasses or moulds ready.
Once the agar mixture has simmered for a minute or two, add it to the blender. Give it a quick blend, then pour the mixture straight into the glasses.
Refrigerate for two hours. Either serve in glasses, or if you've used moulds, turn onto plates immediately before serving. Serve chilled, with extra berries and vegan cream if you like.
The mousse will keep in the fridge for a couple of days.