Having stumbled across the Menhir, the sheep pointed me in the direction of the Barrow, located in the bottom right hand corner of the field, about 200 yards from the stone itself.
Clearly visible from the road, although it's not the most spectacular of barrows, it's there none the less!
In the absence of any name I know of I’ve given it this name. Marked on the OS map (Explorer 106) simply as ‘Tumulus’. I visited this because I thought it was the one mentioned in passing by Craig Weatherhill in “Cornovia: Ancient Sites of Cornwall & Scilly” (Cornwall Books - 1985, revised 1997 & 2000) as an “unusual barrow at SW974683. 1m high and 22m across, the mound is encircled by a ditch and outer bank, giving the monument an overall diameter of 34m”. However, the barrow I visited is clearly at SW976682 and doesn’t have any ditch or bank that I could see. Lots of cow shit all around it and a dip in its top, full of cairn-like stones, but no bank and ditch. In the area the OS map does also say ‘tumuli’ up towards the actual wind farm so maybe that’s what Craig Weatherhill means?
Technically I was trespassing but it is tantalising close to the road and a farm gate, and the field had no crops or livestock, so I took a quick look without asking.