Bankers' Bonanza
All answers contain the name of a river (nothing to do with money)
1. Santa's gratuity for Yuletide banker in Suffolk.(9,3)
2. Selkirk banker puts missile in watery mixture. (6,5)
3. Man in lime tree became this viscount. (4,8) Maybe lord or earl?
4. The Italian banker on the bridge, perhaps, makes commitment to action. (8,3,7)