As far as I understood a Brit Passport doesn't require a visa, but because we on a private flight, apparently you do!
Actually the situation for the US never changed - everyone requires a visa.
What they did was introduce a "Visa waiver" program under certain circumstances; defined passports, travel on an approved airline and a roundtrip ticket.
Try flying with BA on a one-way ticket and you will be told that you need a visa. Private aircraft are not "approved" for the program.