In the UK, there are few restrictions or laws for where you can scatter ashes.
When scattering ashes on private land, you will need the landowner’s permission for the scattering itself, and for future visitation as well.
If you wish to scatter ashes at sea, or at another body of water, this can be done without legal permission. The same applies to national or public parks and other green spaces. We would recommend choosing a quiet location with no crowds; perhaps visit at quieter times for a more private experience.