I’ve planned to go on holiday and the country I want to travel to has been removed from the red list of countries, so I’ll need to quarantine when I return and am unable to. I no longer wish to travel; can I claim the cost of the holiday under section 75?

You won’t be able to claim under section 75 for this, provided your original booking has not been cancelled. This is because the travel company / hotel / airline is still providing the service and you have chosen not to use it. You should check with the company you booked with if there is any flexibility or refund options with the booking you have made.