I realise that the US military offices were there, but ironically this is reported to be the only barrow in the London area that has actually been excavated and proved to be a barrow. If you read my posts this seems pretty clear.
‘Prehistoric London’ by Nick Merriman (1990 – ISBN 0112904475) says that “the only definate prehistoric burial mound (or ‘barrow’) in the London area used to be in Teddington, and was excavated by a group of antiquarians in 1854. It was originally nearly 30m across and 4 m high, and contained at least one central burial (probably a cremation) which yielded a bronze dagger and flints, and various other burials inserted into the mound as later date. Unfortunately, only a few flints survive from this poorly-recorded excavation.”