Stay for 12 months as what? A tourist? There isn’t one. Assuming you are eligible for the VWP, 90 days is more than enough. Although there is no written rule saying you can’t come straight back again, prepared to be denied entry if you cannot satisfy the CBP Officer that you are not trying to live here in 90-day installments. Most people cannot get that much time off work anyway. Once you have been here for more than 180 days in one year you are liable to file taxes here. You don’t want that, do you? What are you planning to see and do that requires more than 90 days? If you are undertaking a coast-to-coast hike or the Appalachian Trail or something then a B-2 might be possible. It has happened before. With that you can stay up to 6 months but they are difficult to obtain. You need a good, solid day-to-day plan and evidence of funding for the entire trip.

The rules have not changed since the last time you asked UK citizen and a year in the USA