Before Coronavirus, deferring your mortgage payments would have been reported to the credit reference agencies by your lender.
The landscape has changed and it now means that it won't necessarily affect your credit score. As this has been agreed in advance, you should not technically fall into arrears. But, before assuming that your lender will automatically apply these new rules, check with them directly. Most major banks have also confirmed that taking a payment break would not affect customers’ credit files.