M_S, it is a bit more complex than that:
Parachute Descents
J5.834.
a. Parachute descents, other than forced descents, are to be made only by:
(1) Trained parachutists whose duties require it.
(2) Service personnel on authorised parachute training courses at No 1 Parachute Training School, or at foreign or Commonwealth military parachute schools with the authority of the Ministry of Defence (SO1 AB/SF Pol).b. Experimental parachute descents are to be made only on the authority of the Ministry of Defence (MAP 12d or SO1 AB/SF Pol).
c. The prior approval of the commanding officer concerned is required for all cases under a. and b.
d. This regulation relates to duty parachute descents from Service aircraft. It does not refer to sport parachuting or adventurous training free fall parachuting at Joint Service Parachute Centres; the orders and instructions for these activities are given in Army General and Administrative Instructions and Defence Council Instructions.
For the Dutch course to be sanctioned as an official military course you need to get CO's approval, and then the approval of SO1AB/SF Pol. This is usually only given to people who are already in date, current British miltary parachutists. There are exceptions, but it is very rare. If you do it this way, it is an approved exchange and it all comes for free.
If you pay your own way, you have bought yourself a space on a civvy run sports parachute course using military type equipment. If you wish to do this as an officially sanctioned adventure training package then you need to follow all of the AT guidelines.
Ask yourself, would you wear US helicopter pilots wings on your uniform because you got a private helicopter pilots licence in the USA? Or a Divers badge because you did a PADI course on holiday?
I am not knocking the course as a way of doing some parachuting, but it is not an official exchange unless sanctioned as above.