Hi Sarah! Welcome to the Disney Parks Moms Panel.
There has been a lot of confusion about this subject! I am also from the UK, and we always use a rental car when taking holidays at Walt Disney World, and enjoy the flexibility it gives us if we are visiting a Resort hotel in the evening for a dinner reservation or if we are park hopping.
Disney Resort Transportation is always available, and complimentary, for every Disney Resort hotel Guest, but sometimes it is nice to have the choice of driving your own car, especially if you do not have much time to spare.
Overnight parking charges have recently been introduced at the Walt Disney World Resort hotels, and Guests will be charged per vehicle, per night of stay, and this will be added to your room charge. Self-parking at the Resort hotels remains complimentary for day visitors enjoying dining, shopping and select entertainment. For residents of the United Kingdom this is slightly different, as parking charges will only apply after 1st January 2020, and if your check-in date is before 1st January 2020, but your stay continues into January 2020 you will not be charged for overnight parking for that stay. The parking charges will vary between Deluxe, Moderate and Value Resort hotels, and all Disney Resort hotel guests will continue to receive complimentary parking at the four theme parks and two water parks.
It's worth noting that if you are a member of the Disney Vacation Club, you will not be charged for standard overnight self-parking when staying at a Disney Vacation Club Deluxe Villa and Disney Vacation Club Members also will not be charged to park when using vacation points to stay at a Disney Resort hotel.
Please come back and visit us if you have any further questions. We will be happy to help. ~ Sue