One down the road from me, a rare large midland barrow must be a contender. Aptly called Barrow Hill. https://www.megalithic.co.uk/article.php?sid=31001
edit, or this one Crookbarrow Hill/Whittington Tump just off the M5.
Though descriptor does say partially man made hill not a barrow specifically.
https://www.megalithic.co.uk/article.php?sid=8065
https://en.wikipedia.org/wiki/Whittington_Tump