Speak with Motability and say during the MOT, it was reported the sidewalls are perished and cracking on all 4 corners. You called KrapFit who just looked at the tyre depth and you then recieved a report via email saying the tread depth was legal. Ask for the tyres to be changed as you don’t feel safe driving the vehicle with perished and cracked sidewalls. Motability will most likely phone throgh to Krapfit and authorise their replacement 🙂
Depending how bad they are on both the inner and outer sidewalls, its an offence to drive with them and with the likelyhood of 3 points per corner if you ever got pulled over for a spotcheck by the police, as once your tyres have perished, their strength and structure becomes compromised in most instances.