Generally speaking, if somebody wants multiple accounts, they can get them easily enough. It would help to know a little bit more about why you're trying to blo

Generally speaking, if somebody wants multiple accounts, they can get them easily enough. It would help to know a little bit more about why you're trying to block multiple signups. I'm in the US, and I write checks to my customers. We're required to submit information to the IRS on a quarterly basis, so we collect payee identification, which is either a Social Security number or Employer Identification Number. It's one thing to lie to an Internet company, its another to lie to the IRS. That discourages a lot of people from trying to game the system. Perhaps there's a similar mechanism available in the UK. Focus on detection. Scoring new accounts for possible/probable fraud, and flagging them for review works wonders. Scaling this approach requires more human effort, but it's worth it when you get in to large dollar amounts. It also helps to have some leverage in your terms of service.