It will depend on whether it is the responsibility of Kent Highways or the Highways Agency; motorways and trunk roads are HA, the others are Kent Highways.
Kent Highways =
kent.highwayservices@kent.gov.uk
If they deem it the Highways Agency, they will send it on to them.
When GaryC posted his complaint on here, I sent that to Kent Highways (above) and they asked for the location of everything that was wrong; after I had replied to that, they said they would forward the email onto the Highways Agency.
Roger