The Future Navy concept is based around five areas of operational output
Continuous At Sea Deterrence
Forward Presence
North Atlantic
Carrier Strike
Future Commando/Amphibious Force
These overlap of course - in particular the last three. The carriers will routinely carry Royal Marines and can be used as an LPH, and the carriers are suited to Atlantic operations and providing ASW and air defence for a task group or crisis response shipping. On that note: