No matter what, you must send your US passport in when applying for a provisional license. You can have the DVLA certify your photo and send your documentation to Swansea if you've been here less than two years and don't know anyone who can sign your photo. If you've been here more than two years, you must have someone on the list sign your photo and you can then either send the documentation yourself or take it to the DVLA and they will send it for you (either way, make sure you provide a self-addressed special delivery return envelope).