thborchert
If you wish to remain within controlled airspace (Class D or A in London FIR),
Southampton is within controlled airspace (Class D) this joins with Class A airspace.
See attached link for outbound routings, GWC can be expected as your first waypoint.
http://www.ead.eurocontrol.int/eadba...2010-11-18.pdf
If you are unpressurised and unable to cruise above FL100, expect a southeast routing to go south of Gatwick.
You should expect to climb at your best rate until passing FL55, thereafter you are into Class A airspace.
ATC at Southampton/Solent are very good. If they see that your rate of climb is low and may result in you leaving controlled airspace before reaching FL55, they will give you an extended routing to ensure that you remain inside.
I would suggest that if you cannot acheive an intial rate of climb 1000 FPM or greater, tell ATC. This will assist them with determining a routing that will ensure that you remain inside controlled airspace.
If you wish to route under Class A airspace after leaving the Solent CTA plan to route GWC-SFD remaining below the London and Worthing CTAs. An FIS service is available from London (124.750/124.600). This may require a maximum cruising level of FL50.