Leisure did indeed operate for 2 or 3 seasons, fortnightly. Britannia also flew to Orlando for a time, around '97 or '98, as well as Puerto Plata in the Diminican Republic.
The market has changed somewhat since then though and flights to a few destinations such as Orlando, Montego Bay and Cancun would probably work now - the problem is that STN has never really been a significant player for the major charter companies, TOM are packing their bags and MYT have already left.