BA used to use one of there ATP's to do paper charters between GLA and BFS, obviously this has stopped but the a/c would be stripped of seats, do the job and be refitted with seats in an evening ready for scheduled pax trips in the morning.
Don't think (could be wrong - Missus says I'm always wrong!) we do anymore, but BA does have a 747-400F in BA livery for freight but I'm sure this is only leased to BA and is owned by someone else (G-KILO is the regn)