Disks and pads are not warranty items but since Motability cover all maintenance costs then they replace them as needed at your local dealers either during a service or if needed you can book in and have them done if urgent, still covered with the cost of the lease.
Do not let Krap Fit touch the brakes(or anything except tyres) as firstly you would be charged and secondly Motability would insist the dealer swapped them out(even if new fitted) and refuse to reimburse Klap Fat for the work and lastly, I wouldn’t trust them to take a piss without getting it on their shoes!