The sheet that does the work
The French pages are the visible part, but the sheet behind them is what an official reader looks at first. On it the translator names the document, states that the French matches the source, and signs and dates the claim. Strip that sheet away and the rest is just text. Keep it, and the set becomes a record someone can act on.
Stamps, seals and the parts nobody translates
A seal is not words, so it is not turned into French — it is described where it sits. The same goes for a wet signature, a punched hole, a watermark or a smudged rubber stamp. The French page ends up as a map of the English one, marked in the same order, so a reader can match them line by line and see that nothing was quietly left out.
The rate, and the clock
Price follows the paper: £25 for each side as issued, so a folded certificate printed both ways counts twice. Time follows the scan. From a clean image, standard work runs 2–4 business days, and express brings it down to 24–48 hours. A dim phone photograph is the one thing that reliably adds a day, because every unclear name has to be queried before it can be written.
Getting the English page right first
Settle the English side before any French is written. If a name is spelt two ways across your papers, decide now which spelling is the one on your passport, because the translator follows the source exactly and will not quietly tidy it. If a record is worn, torn or has been amended, order a fresh copy from Derby Register Office and let the work start from that.