To travel to the USA you need a valid UK passport and an ESTA - it is an electronic clearance that they see when you get to immigration and means they have already checked you against all their records and know you aren't banned from the USA for any reason. You don't need a visa in the way you do for China, for example, where you fill in a form that goes to your national Chinese embassy and they put a stamp in your passport but it IS a visa in a sense - you have permission to travel to enter the USA. It applies for certain countries including the EU and Australia and NZ amongst others (the are listed on the second site I've given you the link for). Travellers from other countries need visas. I doubt it will change when the UK leaves the EU. You now also will need one for Canada if you want to go there to.
This is the link to the US site (which is being maintained this weekend) where you fill out a form and pay, it costs $14 from them.
and this next site will answer a lot of your questions (but DON'T use it to apply for the ESTA because it will cost you a lot more, the $14 plus £32.40 for their "service", they are a business, not official at all, they just make it look like that.)
We recently travelled to Canada and the USA. We applied for our Canadia ETA ourselves but our travel agent did the application for the ESTA as part of the service fee for booking the tours we combined for western Canada and Alaska. My husband has always applied for his ESTAs himself and never had a problem.
Of course you then need your flights to wherever you want to go, the same as flying to Spain or anywhere else. The most important thing for going to the USA and Canada though for you will be travel insurance that covers you fully for your existing illnesses - medical treatment in the USA is amazingly expensive and YOU will get the bill if you need it and haven't valid insurance - and that means you have declared EVERYTHING. If you don't tell the insurer and need medical help for anything, whether it is to do with what you didn't declare or not, the insurance company are likely to refuse to pay. Travel insurance for people with pre-existing illnesses can be very costly - you will need to shop around to find the least expensive. Your current UK health cover within the EU won't be of any use anywhere outside the EU.
I am not sure about visa's but, I have been there several times to L.A. It is a beautiful place and it is also an ugly place. If you go to Santa Monica do it on a Saturday, that is when the street entertainers are there. Plan to have lunch on the pier, and ride the Carousel also.
California is one of those places that, 👣It's a nice place to visit but, I wouldn't want to live there👣.
All you need is a valid passport. I'd recommend seeing San Francisco, Monterey and San Diego. I'm from the State of Montana.
Tom
Under the US Visa Waiver Program, many British Citizens holding a UK passport do not require a US visa providing: Duration of stay is not more than 90 days and traveller holds a valid ticket for onward or return travel. Passport is valid for at least 90 days from date of entry into the United States.
Content on HealthUnlocked does not replace the relationship between you and doctors or other healthcare professionals nor the advice you receive from them.
Never delay seeking advice or dialling emergency services because of something that you have read on HealthUnlocked.