A UK ship has already completed loading an under-deck bulk cargo of cement, drill water, etc. before completing the discharge of a back-loaded deck cargo, and consequently appears to be overloaded. Is this permitted, since she is in port?

No. A UK ship marked with load lines must not be so loaded that: (1) if she is in salt water and has no list, the appropriate load line on each side is submerged; or (2) in any other case, the appropriate load line on each side would be submerged if she were in salt water and had no list, (e. g. as in the question, where she is in dock water).

 The fact that the vessel is not intending to proceed to sea is immaterial: a ship must never be overloaded by more than her dock water allowance plus an allowance for down-river consumption of bunkers, water and other consumables on her way to sea.