I disagree with this. Trunk roads are defined in OSM as "Note that highway=* distinguishes roads by function and importance rather by their physical characteristic and legal classification" https://wiki.openstreetmap.org/wiki/Key:highway

Havelock Road is not an OSM trunk road as it cannot be used southbound by most motor vehicles. Thus it does not fulfil the function and importance test of highway=trunk. (It may or may not legally be a trunk road, but that is not of consequence to OSM). Northbound there is more of an argument, but there are no road signs routing London-bound drivers up Havelock Road. (The signposted route from the coast is via Albert Road, Queens Road and St.Helens Road)

Separately, and as supporting evidence, the road has no green signs at either end.

Entirely removing the oneway restriction tags is also incorrect, as OSM now does not record the actual restrictions on the road.

This is obviously a weird case, but I don't believe we do anyone any favours by letting the map suggest that drivers from London to the coast should go via Havelock Road.

FWIW, there is a third option, which is to mark the route via Devonshire Road, South Terrace, Queens Road and Albert Road as highway=trunk for southbound traffic which is the signposted (non green-sign) route to Folkestone. I personally think that is worse than simply terminating the trunk road at the Priory Street loop as I did.

Feel free to discuss on talk-gb mailing list