Sworn describes a status, not a skill level
The Netherlands works in Dutch, so an English record needs a Dutch text beside it before an office there will act on the contents. What makes this corridor unusual is the second requirement layered on top: Dutch and Belgian authorities look for a sworn translator, a beëdigd vertaler, and not merely for someone who translates Dutch accurately and says so in writing.
It helps to read sworn as a status rather than a grade. A sworn translator has taken a formal oath covering their translation work, and their declaration on your pages is made under that oath. Plenty of excellent translators are not sworn, and that is not a comment on their ability. It simply means their signature does not do the particular job this destination is asking for.
The requirement changes how you plan
On most corridors the translator can be chosen after the scan arrives, because any qualified professional can produce and certify the text. Here the requirement points at a smaller group from the outset, so the sensible order is reversed: settle that the Dutch route is what you need, then book, then send the file. Leaving it until a deadline is close removes the flexibility that makes express turnaround useful.
The cost follows the same logic. A certified translation into Dutch in Nottingham on this route runs at about £25 for each page of source paper, above the rate you would see where an ordinary certificate suffices. Pages are counted by sheet, so the arithmetic is easy to do in advance once you know how many sides of paper are genuinely in scope.
What the oath does not reach
A sworn declaration speaks to the Dutch text and its relationship to the English document supplied. It says nothing about whether the English record is accurate, whether an entry has since changed, or whether the particular office receiving it will be satisfied on other grounds. An oath makes a translation dependable; it cannot make a flawed source sheet into a sound one.
So the source is worth choosing carefully before any Dutch is written. Where the record is a civil one registered in this city, Nottingham Register Office issues a fresh certified copy of a birth, marriage or death entry from The Council House, Old Market Square, Nottingham NG1 2DT, so a clean and current sheet can go to the sworn translator while the original stays with you.