There were two Harradine families living in Southill in the 1801 census:
James Harradine who shared a house with an Isherwood family. 2 families, 4 males, 2 females, 2 employed in agriculture, 1 in trade. Impossible to know with any certainty if James was single or married - a Robert & Frances Isherwood baptised a son in Southill in 1800. They only married in Southill in 1799 so my interpretation, which might be wide of the mark, is that there were two families each with 3 members in it (Later: they were connected - Frances Isherwood was née Harradine, but I can't find her baptism)
and
John Harrowdine, 1 family, 3 males 3 females, 2 employed in agriculture, 4 not working in either agriculture or trade. I can't see who this family was so can't rule out the possibility that James was a part of it and therefore wasn't the 1783 Old Warden James whose father was James.
With baptisms that I can't trace, pointing to possible non-conformity, of which there were a number in Southill (as Jan and I know to our cost!), unless you have a firm link to James in Old Warden I don't think you can assume that he is the right James