British and other EU citizens who want to enter the USA as a tourist will need to apply for an ESTA visa waiver programme. The ESTA grants you 90 days of travel, and grants you multiple visits to the USA for two years. This will cost you $14. You need apply at least 72 hours in advance.
Due to the Trump administration, if you are a dual national of Iran, Iraq, Sudan or Syria, you will be refused entry into the USA. Similarly, if you have travelled to Libya, Iran, Iraq, Somalia, Sudan, Syria or Yemen since 2011, your visa will be denied. The USA is notoriously strict when processing visa applications, so only apply if these conditions do not apply to you.
Make sure to check back here for updates on visa conditions.
If you need more information, contact your local American embassy or visit their official website.