DVSA has sent out an email relating to Coronavirus. I suspect this is especially for the idiots still intent on doing lessons and tests, even if they are unwell.
Basically, do not take anyone to test if you or they feel unwell. Test rearrangements will be free of charge, even if at short notice.
You need to call 0300 200 1122 (8am to 4pm, Monday-Friday) if it’s a short notice cancellation.