Inside the treaty, and outside it
Every country decides for itself how much to trust a foreign signature. Those inside the shared treaty accept a single slip from one another and ask no more. Those outside it keep the older habit of having their own officer look at each file. Cambodia belongs to the second group, and that single fact shapes the whole route.
Cambodia's standing on the Convention
Cambodia has not joined the Hague Apostille Convention. A paper bound for Phnom Penh, Siem Reap or Sihanoukville requires embassy legalisation once the British mark is on it. The sequence is not negotiable: the consular officer wants to see the British mark already there, so a file sent in the wrong order simply comes home again.
The British half, seen from Cardiff
A single office covers the country and does everything through the post, so nothing about this stage happens in Wales. It marks register copies, court copies and papers signed by people whose signatures it already holds, then returns the file. An apostille from United Kingdom to Cambodia starts here and this part is cheap and predictable.
The per-paper charge makes the choice of contents the real decision. A teacher heading out may need a degree and a police record and nothing else. Trim the bundle before it goes and both the British fee and the consular wait shrink with it, since fewer sheets mean a shorter file at every desk.
Khmer, and the timing of the words
Public offices in Cambodia work in Khmer, though English is widely used in business and tourism. Where a ministry or a court is the reader, a Khmer version should sit with the file. Have the words done after both stamps are attached, so what the translator describes is the completed bundle and not a bare sheet from months earlier.