1. A method of conditionally executing branch instructions which comprise an opcode field defining a type of test to be applied to determine whether or not to execute a branch operation, a control field designating a control store holding a plurality of indicators, and a destination field holding information on a branch target address, the method comprising: determining from the opcode field whether or not the test will check the state of one indicator or a plurality of indicators in the designated control store; accessing the designated control store to check the state of said one or said plurality of indicators depending on the determination; and generating a branch target address using information in the destination field in dependence on the state of the or each indicator checked.