Within a system supporting execution of variable length instructions a program is stored within discrete memory regions with a variable length instruction spanning a gap between two such discrete memory regions. When execution is attempted of such a variable length instruction spanning a gap, an abort handler is initiated which serves to copy the end portion of one of the memory regions together with the start portion of the other memory region into a separate fix-up memory region where these may be concatenated such that the whole of the variable length instruction will appear in one place. Execution of that variable length instruction from out of the fix-up memory region can then be triggered. This execution is constrained by the setting of a single step flag which causes the hardware to only execute the single instruction which span the gap before returning control to a single step exception handler which can then restore program flow to the point in the following memory region after the variable length instruction which spanned the gap.