Under no circumstances should you attempt to fool or deceive US immigration authorities. The consequences could be serious, and would at the very least involve your immediate ejection from the country.
Talk to the US embassy in London, and follow their advice. If they advise that you need a visa, the procedure is explained in detail in the 'sticky' post at the top of this forum. I understand that the procedure takes about 4 weeks.
Why jeopardise your holiday out of laziness?
Scroggs Virgin/Wannabes Moderator
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