If no further movement is likely, then you can just gob it up with mortar, mesh over the front and then plaster away.
If movement is likely then helibars may be the answer but it depends on whether potential movement is up and down or sideways - but in this scenario you would have to deal with the cause of movement and not just the crack.
But in context of a major refurb, you may think it worthwhile to install some helibars for good measure. But the issue is whats on the other side of that wall? The surveyor says its not cracked, but a proper job would need bars inserted from both sides and every 225-300mm up the wall, and not just on the inside face.