Cities aren't a meaningful administrative unit in England. The previously and correctly tagged admin_level=8 corresponds to "Metropolitan districts, non-metropolitan districts, London boroughs". 

In England, admin_level=10 is used for parish councils.

Please read the following before you "correct" any further administrative boundaries.
https://wiki.openstreetmap.org/wiki/Tag:boundary%3Dadministrative#admin_level=*_Country_specific_values

As this could break queries, I have reverted your changeset.
https://www.openstreetmap.org/changeset/153122564