I've booked a Fjords cruise for this August with my wife and daughter, with the three of us in one cabin. Since we booked, near the end of last year, my daughter decided that actually she probably doesn't want to come, so I emailed Cunard to ask about cancellation charges. Cunard has responded that the standard fee applies which is 15% of the cost for my daughter, which comes in at just under £120.
I appreciate that we have to pay some sort of fee for the inconvenience caused to Cun