Wally, is this list of UK 7000-ser SSR allocations of any interest to you:
7000................Conspicuity code
7001................Military Fixed-wing Low Level Conspicuity/Climbout
7002................Danger Areas General
7003................Red Arrows Transit/Display
7004................Conspicuity Aerobatics and Display
7005................Autonomous military operations within active TRAs
7006................Autonomous Operations within TRAs
7007................Open Skies Observation Aircraft
7010................Operating in Aerodrome Traffic Pattern
7011-7013.......Not allocated
7014-7027.......UK Domestic
7030-7045.......RNAS Culdrose
7030-7047.......Aldergrove Approach
7030-7057.......TC Thames/TC Heathrow
7030-7066.......Durham Tees Valley Airport
7030-7077.......Aberdeen (Northern North Sea Off-shore)
7046-7047.......RNAS Culdrose Conspicuity
7050-7077.......RNAS Culdrose
7067................Durham Tees Valley Airport Conspicuity
7070-7076.......TC Thames/TC Heathrow
7100................LTCC and LACC Saturation Code
7101-7177.......Transit (ORCAM) Brussels
7200................RN Ships
7201-7247.......Transit (ORCAM) Vienna
7250-7257.......UK Superdomestic for destinations in France and Barcelona FIR
7260-7267.......Superdomestic - Shannon/Dublin to France and Spain
7270-7277.......Plymouth Radar Superdomestic for destinations in UK and France
7300................Not allocated
7301-7307.......Superdomestic - Shannon Eastbound landing UK
7310-7327.......Superdomestic - UK to Netherlands
7330-7347.......Superdomestic - Netherlands to UK
7350...............Norwich Approach Conspicuity
7350-7361.......MoD Ops in EG D701 (Hebrides)
7350-7367.......RNAS Culdrose
7350-7373.......Manchester Approach
7350-7377.......Bournemouth Approach/LARS
7351-7377.......Norwich Approach
7362................MoD Ops in EG D702 (Fort George)
7363................MoD Ops in EG D703 (Tain)
7374................Dundee Airport Conspicuity
7375................Manchester TMA and Woodvale Local Area (Woodvale UAS Conspicuity)
7400................MPA/DEFRA/Fishery Protection Conspicuity
7401-7437.......UK Domestic
7440-7477.......Superdomestic Spain and France to UK, Ireland, Iceland and North America
7500................Special Purpose Code - Hi-Jacking
7501-7537.......Transit (ORCAM) Geneva
7540-7547.......Transit (ORCAM) Bremen
7550-7577.......Transit (ORCAM) Paris
7600................Special Purpose Code - Radio Failure
7601-7607........Superdomestic - Shannon/Dublin to Nordic States
7610-7617........Superdomestic - Ireland to UK
7620-7657........Superdomestic - UK to USA, Canada and Caribbean
7660-7677........Superdomestic - UK to USA, Canada, Canaries and Caribbean.
7700................Special Purpose Code - Emergency
7701-7717.......Superdomestic - UK to France and Spain
7720-7727.......Transit (ORCAM) Munich
7730-7757.......Superdomestic - Shannon Eastbound landing UK
7760-7775.......Superdomestic - UK to Channel Islands
7776-7777.......SSR Monitors
That was the list as of a couple of years ago - the current list is in the UK AIP ENR 1-6-2-10.
7760 is/was not a 'special purpose' code and has no significance.