I also didn't now of a recent website of Martin's, and the family website watersoncarthy.com discontinued in May 2017 or earlier.

But Kevin Boyd's Martin Carthy fan websites "Come Sing It Plain" and "The Martin Carthy Broadcast Archive" seem to have gone recently - when I go to them I get a standard Wordpress page telling me "This site is marked private by its owner."   Maybe that's what Jack was referring to?