I thought there was just one, Bishop John Saxbee of Lincoln, but could have been out of date. Then I found this and it seems to confirm it.
http://www.churchsoci...tional_bishoplist.asp
Could it be a trick question. There are two others - David Rossdale, Bishop of Grimsby, and Timothy Ellis, Bishop of Grantham both of whom come under the category of Bishop Suffragan, and both still part of the Lincoln Diocese