Staffing an air traffic control tower is an expensive business. The technology has recently been developed to allow air traffic control to be delivered remotely. Sweden was an early pioneer of this approach. A series of high definition cameras on the airport combined with high speed data links to a remote facility that is already well staffed means that an airport can be controlled by staff many miles away. This is the approach London City Airport now has taken.
The controlling staff for LCY are now based at Swanwick in Hampshire rather than on the airport itself. No doubt, this is cheaper than having London based staff in the quantities required. It also means that the low traffic levels that LCY has are not having to be covered by an unnecessarily large staffing level locally if the Swanwick staff are able to provide the necessary cover for what is not a busy airport. The visibility of what is going on at the airport is provided by high definition video feeds and there is a tower at LCY which is the one that provides this coverage. I got to see it when I was walking along the south side of the docks near the runway. It will be interesting to see how approaches like this get developed for more airports that need air traffic services but do not have the volumes to justify the staffing involved.