You need an export permission from the home office, and an import permission from the Dutch authorities. If you do it any other way, you're at the mercy of the border guards.
Actually seems like if you get that Apostille'd, you might not need it. Best to call your clinic and doublecheck, but this is what I found
If you are traveling with a personal amount, follow these steps at least 4 weeks before you go:
Request a Travel Letter: Ask your clinic for a travel-specific letter. Ensure it is signed by your doctor (wet-ink signatures are sometimes preferred over digital, though e-Apostilles are now common).
Get an Apostille: Submit this letter to the UK Government Legalisation Office. You can choose a paper-based or e-Apostille. This is the "official" stamp that makes the document legally recognizable to Dutch Customs.
Carry Original Packaging: Your cannabis must remain in its original pharmacy container with the dispensing label clearly visible and matching your ID.
Hand Luggage Only: Always carry your medication and documents in your hand luggage. Do not put them in the hold.