I think Bookworm may be right about caution on the Special Branch designation from the GAR list.
The position re Shoreham though should unambiguously sourced by following the advice here
http://www.sussex.police.uk/online_forms/ports_unit.asp
Here is the list of dedicated ports from schedule 7, no sign of any update at this point and no sign of shoreham on the list
Aberdeen
Biggin Hill
Birmingham
Blackpool
Bournemouth (Hurn)
Bristol
Cambridge
Cardiff
Carlisle
Coventry
East Midlands
Edinburgh
Exeter
Glasgow
Gloucester/Cheltenham (Staverton)
Humberside
Leeds/Bradford
Liverpool
London-City
London-Gatwick
London-Heathrow
Luton
Lydd
Manchester
Manston
Newcastle
Norwich
Plymouth
Prestwick
Sheffield City
Southampton
Southend
Stansted
Teesside