Repairing cracks in new plaster

Hi unfortunately without seeing the work and the cracks it's very difficult to say what the cause is or offer advice on the best way to fix it. Small cracks often appear on new plaster if the plaster drys out to quickly was the heating on high is the room normally above average temperature?. Was the walls sealed properly to prevent the new plaster drying to quickly?. Was out of date plaster used? Is there a room above? As the cracks along the top could be due to movement on the joists all just possible things but without seeing the job it's hard to say exactly like I said before. My solution would be to contact the plasterers who did the job for you get them back as I'm sure they will come take a look and advise you on what the problem is and if necessary re-due the work at least give them a chance. Hope this has helped Thanks grant G. M. E property renovations

You can basically take out the cracks with a Stanley knife blade and Pva the cracked area Tape the crack allowing the Pva to fully dry and place fibre tape scrim over the crack and then apply a thin binding undercoat plaster and finish with multi finish plaster feathering out to the existing wall

There is a product called make good b and q sell it that will sort out the crack as to why the cracks have aperd it could be a number of things but as a guest I would say the plastera has not scrimed the ceiling line. And may be not pva the walls hope this helps kind regards

Fill the cracks with easy fill then sand down and repaint the area