I've just found the report I produced and that showed that each employee at LCY and SOU served 4.5 ppd and BHX served 3.8 ppd. These figures were for 2009.
With SEN at 2 mppa I projected it would need 1,200 employees, excluding all the MRO and other aviation related businesses active on the airport, so that would be 4.6 ppd per employee.
So if 5.4 passengers per day per member of staff are being processed at SEN at the moment they are operating more efficiently than I predicted, but this may be accounted for by technology changes and less hold baggage etc. since 2009, so requiring less staff.