Same here. With me it happened when Virgin Media changed my IP address.
I now have a file /etc/dnsmasq.d/99-my-settings.conf in which I have added:
server=/**.gov.uk/1.0.0.1
server=/*.tv/1.0.0.1
and then restarted dns
(There should be a single asterisk on that first line )
It appears there is a problem routing to the name servers authorative for these domains from Virgin's network. My Pihole now uses 1.0.0.1 to lookup just these domains instead of using unbound.