Note Control
Check this website. https://tristandc.com/shipping.php Remember tourist has the lowest priority (priority class 8)
If you are in category 4 to 8 above, you may be required to give up your booking and defer your travel to another sailing for those covered by category 1-3.

Then read this link:
https://tristandc.com/visitsorganise.php
Second Step : Permission

Have fun