Well said Pilgrim

As English Heritage have now announced that the, "...foam is extremely limited in extent... (with) a light yellow colour, which acts as a marker and ensures that all of this material can be removed..." it would seem that they have at last realised that leaving alien objects in Silbury is unethical.

Perhaps English Heritage would now confirm, either here or on their Silbury Updates webpage, that their plans to leave a time capsule, the 1968 Atkinson/BBC door and lintel, and other alien objects within the structure have now been abandoned.