The records this applies to
Zambia runs its public business in English, so the deciding question is the language your record was issued in. A UK paper usually needs nothing at all. The files that do need work came from somewhere else and now sit in a drawer in Wolverhampton, waiting to be read by an employer or a registry that works only in English.
English, and how much of the page is reproduced
A certified translation into English in Wolverhampton sets out the entire sheet rather than the parts that look important. Seal wording is written out in words. Revenue stamps, serial numbers and notes in a margin all appear. Where handwriting cannot be read with confidence, it is marked illegible, because a guess that later proves wrong causes far more trouble than a gap.
What the certificate of accuracy does
The route used is a certified translation with certificate of accuracy. That certificate is a signed page in its own right, naming the translator, the direction of the work and the date. Attached to the English text, it turns a private rendering into a certified translation for Zambia that an office is willing to file and act upon.
Rate, page count and speed
The rate is roughly £25 / page of source, so a dense page and a sparse one cost the same. Standard work takes 2–3 business days, with 24 hours available where a start date is close. The clock begins on a readable scan, which is why a flat image beats a photograph taken at an angle every time.
Fresh UK records, and the check in Lusaka
Where a UK civil record forms part of the file, Wolverhampton Register Office at Civic Centre, St Peter's Square, Wolverhampton WV1 1RU issues new certified copies of births, marriages and deaths. Sending the fresh copy keeps your own record at home. That office issues records and plays no part in translating or certifying them.
In Lusaka the certificate is read first, the pages are counted next and the names are matched last. An official English translation in Wolverhampton is accepted on being complete, dated and signed. Gaps are what stop a file: an unscanned reverse, a missing annex, a stamp cropped away at the edge of an image.