With respect to Sierra Leone.....
http://www.britains-smallwars.com/Si...ne/forces.html
http://www.navynews.co.uk/articles/2...0000051901.asp
We deployed a CVS (to carry aircraft - obviously), a LPH (operating helicopters), two frigates to provide naval gunfire support (if needed), a stores ship (and tanker?) to support the RN group plus two LSLs to support the ground forces. One of the frigates was in the area already and the LSLs were there to support the ground forces. Therefore I think the comment about "hangers on" is not really relevent in a very low risk environment. The purpose of the deployment was largely for political and psychological reasons - noticing a number of large grey ships off the coast was intended to send a signal to both the rebels and the civil population.
Both Sea Harriers and Harrier GR7s were operating and at the time the MOD website stated that they were being used mainly in a reece role and that if necessary, the SHAR could use its 30mm cannons. (Incidently Jacko, can you explain why the GR7 can't take the cannon packs?) Can you imagine the political consequences if UK aircraft had started dropping bombs and firing rockets?
Ultimately it was troops on the ground that were needed, along with support helicopters, much more than combat jets - or ships.