A computer system for executing branch instructions and a method of executing branch instructions are described. An instruction fetcher fetches a sequence of instructions from memory for execution and a sequence of instructions for commencing from a target location identified by a set branch instruction in a sequence of instructions being executed. When an effect branch signal is generated, the target instructions are next executed, and the fetcher which was fetching the instructions for execution commences fetching of the target instructions. At least some of said instruction strings further include a condition instruction which defines a condition and determines that further instructions to be executed are new instructions only if that condition is satisfied. The system includes also a select circuitry to execute the new instructions if said condition is satisfied.