Hello Michelle and welcome to the Disney Parks Moms Panel where it's always an added pleasure for me to assist a fellow Guest from the United Kingdom with their jolly holiday plans to visit the magic of Walt Disney World Resort.
I totally understand your query and like you, I wouldn't personally wish to carry my all important British passport with me at all times either! Florida law does indeed state that adults wishing to purchase and enjoy alcoholic beverages must be aged 21 years or older and I have to tell you that even though I'm obviously way past my 21st birthday, I have been asked to prove my age whilst in Orlando!
However I've some great news for you! You'll be happy to know that
International Guests acceptable forms of ID can be either a photocopy or a mobile phone screen shot of a passport as long as it's accompanied by a divers licence or another official form of ID which can be double checked to verify. It's also worth remembering that foreign driver's licences or IDs aren't usually acceptable forms of identification on their own.
I also thought you may find these
Frequently Asked Questions - International Travellers to also be an extra useful planning resource for your upcoming Disney holiday.
Have a great Disney day & cheers!
~ Jane