MBUK sent an email in April 2020 to owners stating that
"The majority of workshops will remain open with a limited team to accommodate breakdowns and the service of key workers’ cars" and gave the following advice about servicing:
If you’re unable to attend a service appointment when your car’s service is due, we’ve implemented a temporary revised limit for overdue services:
For Mercedes-Benz cars, the limit has increased to the sooner of 180 days past the current due date for a service to be completed or the vehicle reaching the 3,728 mileage interval for a service to be completed (previously 90 days / 1,864 mileage interval).
Please be advised that delays to your vehicle being serviced, which are within the temporary revised limits for servicing set out above, will not invalidate your vehicle’s warranty. However, all of your other obligations and exclusions in relation to your vehicle’s warranty remain.
My experience at the time was that as an "ordinary Joe" I couldn't get a service appointment with any of my local MB dealers.