The lenders both made the requests in updates on their valuations process, noting they are on course to complete all on hold physical valuations by 12 June.
Nationwide and its buy-to-let arm The Mortgage Works asked brokers to let them know if clients were not proceeding with their mortgage applications.
Regarding valuations, the lenders said where they had been unable to make any contact, they had either left a message or sent a text to the applicant or vendor/estate agent.
They said before calling about valuations to contact whoever was given for access to the property and to check the details supplied.
Santander also asked for advisers to inform it “urgently” if cases were no longer proceeding.
It said valuations will be booked in chronological order, with the oldest applications booked in first. Once the valuation has been booked, brokers will be informed.
“Please be aware that receiving a valuation booking date may take longer than usual as our valuation partners need to conduct a detailed government safety assessment as part of the booking process. We thank you for your patience.” it added.