Just to say that (due to the fencing along the motorway) you cannot see over Warren Hill from the M4. Perhaps you can get a view from the A48 immediately to the north?
Either way, not sure how you would access this site?
Hemmed in by road and motorway, intruded upon by pylons and buildings, this site stands on a minor eminence overlooking the mouth of the river Nedd and possibly guarding access to the river's navigable lower reaches.
Coflein (J. Wiles 2002):
Warren Hill enclosure is an oval enclosure, originally c.130m NE-SW by 94m, defined by a bank, reduced to a scarp; the north part destroyed by road construction and the interior mutilated by recent activity.
Observation of cuttings indicates that the circuit was ditched and that there was an inner, ditched and ramparted, enclosure.