What is the US ESTA?
The Electronic System for Travel Authorization (ESTA) is a mandatory pre-travel requirement for citizens of Visa Waiver Program countries — including the United Kingdom — who wish to visit the United States for tourism, business, or transit.
ESTA is not a visa. It is an automated eligibility check linked electronically to your passport. Once approved, it permits multiple trips to the United States for up to 90 days per visit over a two-year period, without the need to visit a US embassy.
US Customs and Border Protection retains the right to refuse admission on arrival even with an approved ESTA, but holding a valid authorisation is a strict requirement before boarding any flight or vessel bound for the United States.