OFFICIAL ANSWER:
Irrespective of the type of passport you hold, you're not eligible for the Visa Waiver Program, so you must obtain a US visa prior to travel.
http://london.usembassy.gov/cons_new/visa/niv/ index.html
This involves making an appointment to attend the US Embassy, in London, for an interview. (The waiting time might be several weeks).
You must attend the embassy in person. (Postal applications are not accepted). The whole process takes most of a day. You'll either have to pay US$100, by debit/credit card, at the embassy or you'll be given a form to take to a local bank so that you can make a sterling payment.
The minimum time to hear whether you'll get a visa is '14 to 16 weeks'.
UNOFFICIAL ANSWER:
As Dzug states, if you got in before, there's no reason to think that you won't get in again.
Chris