It is in the UK Booking Conditions
“Should you wish to make any changes to your confirmed holiday, you must notify us in writing as soon as possible. Whilst we will endeavor to assist you, we cannot guarantee we will be able to meet any such request. For guests wishing to make a significant amendment to their booking outside of 90 days from departure, such as changing the ship or sail date, note that a booking transfer fee is applicable. Please note that any amendments for hotels, transfers and flights may result in the loss of the amount that was collected at the time of booking for these additional components. The transfer fee is £75 per guest which is limited to the first two guests on a booking, therefore any additional guests will not be charged as well”