bath basin tap

I would like to replace a one hole basin tap. but don't know how to take it off. From the under the basin I can see no back nut to hold the tap, there is a plate shape like a comma sign, and have three pipes attached to this plate. what tool i can use to remove this plate so i can remove the tap on the top ? thanks

Small box spanner and an extension peice. Can be picked up quite cheaply at Plumb Center, sized for the job