On advice from RePec (Sune) via the Economics Department we today (22 Aug 2018)
1. Copied the nufseri.rdf file to nufseri.rdf.bak.Aug2018
2. Edited the nufseri.rdf file and deleted lines 27-51.  (These refer to the Template for the "Oxford University Economic and Social History Series", Handle: RePEc:nuf:esohwp)
3. Renamed the esohwp folder to be esohwp.for_deletion

N.B. It may be that we need to truly delete the 'esohwp.for_deletion' folder for this not to interfere.

Sune Karlsson's instructions in full:
"I see that the Social and Economic History working papers are still in the Nuffield RePEc archive. Can you please remind them that they need to remove it from the archive. That is delete the template for RePEc:nuf:esohwp from the nufseri.rdf file and delete the esohwp directory from the web server."

Sune replied on 23/8/18 to say that these changes sounded correct.

I also (as part of Sune's follow-up) changed line 11 in nufarch.rdf to a better general URL.  Was: https://www.nuffield.ox.ac.uk/nuffield.html  Now (23/8/18) changed to: https://www.nuffield.ox.ac.uk/economics/