Rhiw Goch boulders lie on land mapped as open access under the CROW Act and is owned by the National Trust, but is leased on a historical farm tenancy, to a local farmer. There is a right of access over the land, on foot for recration that includes climbing.
However that does not mean the land occupier has to provide a means to access the land. The gate has normally always been wired or padlocked shut if i recall as the risk of stock escaping onto the neighbouring trunk road is very real. There is no public right of way through the land, or through the gate, so the occupier is perfectly entilted to padlock the gate.
I'll raise the issue with the local NT Ranger to see if a simple stile or discreet crossing point can be placed here.