On the surface the handling charges at RAF Northolt do seem very high, however if an accountant was to look into this, the picture could look very different...
The rent charges (to become the only handler) at RAF Northolt cannot be cheap... The MoD insist on a large number of handling and security staff to be on duty at any one time to fullfill the contract. No catering vehicles are allowed airside due to new MoD regulations and all catering must be stored in approved fridges then security screened before being delivered to the aircraft.
All in all any military airport is an expensive location to run a business from. Add in the recession and the vastly reduced number of slots being taken at Northolt (no slot requests are being refused at the moment, the uptake is that low!) Actually with all that in mind a £30 handling fee for catering doesn't sound like enough to break even!
And here is another angle. One of our clients recently left a bag behind in the lounge at Northolt. The Jet Centre took full responsibility for their staff not checking the room after the pax left and flew the bag to Nice on the next BA flight (together with a member of their staff). Quite exceptional customer service and I doubt that other FBOs in London would do the same?