It usually depends on whether or not the bookmaker is able to verify your account details (address, date of birth etc) using a third-party database. If you are resident in the UK, this can often be done by checking you on the electoral register. If you are not resident in the UK, however, the bookmaker might not be able to verify your details via a third party and so will ask you directly to provide them with proof of your identity. At this stage I don't think you should read anything sinister into Winner's request. If you provide them with satisfactory proof of your identity, then I would expect you to get paid without any problems.