Good question. Depends if there's other work being done at the same time, but just changing the tails with no other work is minor work that does not require an EIC. In general, an EIC is required for major changes, like a CU change, or new circuits added to an installation.
Some may choose to issue an MEIWC (minor electrical installation works certificate) for small jobs, really just to set bounds to the work that was done as an arse covering exercise. I believe that the various Part P cartels may set guidelines as to when an EIC or MEIWC might be used by their members, but that would only apply in Part P land, so not Scotland (not sure about NI).