40mm over is not going to cause any planning problems, i presume your width is 4000mm 18 bricks is 4040mm so you would need perps of less than 8mm on 215mm bricks if sticking to 4m and tightening back, another problem with smaller perps can be doors/windows already made to brick size ie 1810mm, your opening would be 1790mm, but as already mentioned a decent brickie would be able to set out to best suit your plans/bricks/openings. I always set out to brick gauge, to cover myself if things don't fit etc, brick can vary 8mm within tolerance, so you could set out using 211mm brick then try laying 219mm on top.
