Why navies maintain contingency plans for hostile ports

Does the modern Royal Navy still plan how it might attack hostile naval bases?

Yes; maintaining assessments and options for likely threats is normal staff work. No particular current attack plan is identified.

The Royal Navy is described as maintaining plans for likely threats and possible operations against enemy ships and bases. Keeping the threat assessment current is part of that staff work. The existence of contingency planning is presented as ordinary naval practice and is not itself a secret. No particular current operation or detailed attack plan is identified.