I don't know if offshore work to the same rules as circuit.
You start with a basic license and you have to compete in 5 club races .
With your license you will have received an upgrade form which you need to get signed by the OOD at the end of the meeting.
You then send this off to the RYA to upgrade to National license.
With this you will receive another upgrade form which will need signatures from 3 National races so that you can upgrade to International.
Hope this is of help.
Your best phoning the RYA and speaking to John or Nikki who will be able to help you.