This makes good reading. It is the Royal Aero Club's reaction to the imposition of the February 1913 Aerial Navigation Bill - it is regarded as 'evil':
http://www.flightglobal.com/pdfarchive/view/1913/1913%20-%200727.html
It seems the main thrust of the Act was to restrict flight paths over populated areas for safety reasons, but also to prevent foreign pilots from flying wherever they wished for the purposes of espionage. It set up prohibited areas over which pilots could not fly or they could be shot at, the aim being to protect the public. Presumably the military areas of Dover Castle, Archcliffe Fort and the harbour overnight became no-fly areas. This would have caused a headache for amateur flying clubs engaged in cross-channel flying as British airspace effectively became closed with landing prohibited without specific permission.
An amendment to Act was made on the 18th July 1914 in response to the Daily Mail "Circuit of Great Britain" race:
"Aerial Navigation Acts, 1911 and 1913.
The Secretary of State hereby grants the following Exemption
from the Orders under the Aerial Navigation Acts, 1911 and 1913,
made by him March ist, 1913, and May 25th, 1914:—
Seaplanes taking part in the Daily Mail Circuit of Great Britain
Race, 1914, may, during the course of the race, pass within the
following prohibited areas, subject to the conditions specified below:—
2) Dover Castle and Archcliffe Fort: on condition that no competitor shall pass nearer the shore than a distance of 800 yards seaward from the end of the 'Admiralty Pier, nor at a height exceeding 300 ft."