Do UK food standards enforcement officers have powers to inspect ships in UK ports to enforce food safety legislation?

Yes. 

The Food Safety (Ships and Aircraft) (England and Scotland) Order 2003 (and equivalent Wales and Northern Ireland legislation) extends the meaning of “premises” in the Food Safety Act 1990 to give “authorised officers” powers of entry to certain ships to enforce parts of the Act as well as The Food Safety (General Food Hygiene) Regulations 1995 and The Food Safety (Temperature Control) Regulations 1995