The inspectors report linked at #2204 is worth a read - the application seems to have been based on efficiency rather than safety. The inspector doesn't seem very impressed with the application and as cavokblues has mentioned has virtually told them what to put in the next application.
34. The Civil Aviation Authority (CAA) has also suggested that the trees to be felled are affecting flight operations at Southampton airport. Referring to the UK’s obligations under the Chicago convention, it pointed out that the airport is required to have procedures in place to ensure that the air space surrounding the airport remains safe at all times. The airport appears to have achieved this through weight restrictions placed on aircraft using its runways.
35. Nevertheless, and in this context, the CAA has referred to 95 tree obstacles at Marlhill, which supposedly penetrate the airspace around Southampton airport. It has also pointed out that the mitigation taken to compensate for this is resulting in airline inefficiency, due to them incurring seat penalties etc. It then goes on to refer to the safeguarding protection that the Secretary of State has afforded to Southampton airport, because of its importance both to the national transport system and the local economy