Greek is what Greece reads
Greece works in Greek, so that is the language your paper is turned into for use there. A certified translation for Greece sits beside the English document rather than replacing it, and the English stays with you throughout. What comes back is a Greek text with a name, a date and a signature on it, written by a translator qualified to sign.
The claim is narrow on purpose
A signed statement of accuracy is a small, precise thing. It says that a named person read the English, wrote the Greek, and stands behind the match between them. That is the whole of it. The narrowness is a feature: a claim that tried to cover more would be a claim nobody could honestly make, and a reader who knows this can weigh the file properly.
It follows that the translator is answerable for one kind of error and one only — a word carried across wrongly. If a date is wrong on the English page, the Greek carries the same wrong date, and that is correct behaviour rather than carelessness. The two versions have to agree, even where agreeing means repeating something you wish the paper did not say.
Four things it does not do
It does not test what the paper claims. Nobody rings a school or an employer to see whether a line on the page holds up. It does not renew anything either: a signed Greek text has today's date on the signature, while the record underneath keeps the date it always had. Certifying words changes nothing about when the record was made.
It does not raise a document's rank, so an informal letter stays an informal letter in Greek. And it does not decide anything at the far end — that call belongs to whoever opens the file. What it does is remove the one obstacle you can actually remove in Sheffield, which is that the reader cannot read English.
Cost and timing
Pricing runs at £25 a page and the count comes from the scan, so you know the size of the job before it starts. Standard work is 2–4 business days; the express route lands in 24–48 hours. Both give the same signed Greek set, and the faster one buys time in the translator's week rather than a different standard of work.