Hi. It could maybe be settle meant cracks. But also if they have used steel lentals over the windows and door they can expand with the heat

Rake out the cracks, go as wide and deep as necessary, spray water into them with a spray bottle, fill them with Dry wall adhesive (available at B&Q) making sure you apply with good pressure over and over again until you see the "filler" try to bulge back out a little, let this dry, sand back and perform a final fill with TouPret T110 filler (available at screwfix) sand to a finish when dry, apply a watered down coat of matt emulsion thinly just to seal the work, then when completely dry use a tube of "Sticks Like s##t" in white (From Screwfix) to apply a thin bead along the length of the corner abutments to ceiling etc, wipe this in with pressure using a finger, when dry decorate as usual.

I’m not sure what ceiling rages is but if they mean ceiling cracks it could be under-sized joist or un-strapped joist

Given the age of the property, I suspect this is a timber framed house and not blocks and mortar to the inside walls. timber always shrinks and expands with humidity changes but to be honest would need a site survey to confirm