I want to make sure that you are aware that requests for a "TAF" (Traveler's Allowance Fee) or "BTA" (Basic Travel Allowance) are most often part of a widespread type of internet fraud.
Usually this is part of a "Romance Scam" type of scenario, in which someone strikes up an online romance, eventually promises to visit in person, and then asks the victim to forward this TAF money.
There are some other variations on the scam, in which the travel is for purposes related to promises of a job, an inheritance, lottery winnings, etc. etc. - but they are all basically the same thing.
Typically once the TAF or BTA money is wired, the scammer will contact the victim with a new story about a family or medical emergency that prevents his/her travel (and that usually requires additional funds for "emergency surgery" or the like.)There is no legitimate requirement for a TAF or BTA to travel from the UK to the US
Now, it is true that an applicant for a travel visa may in some cases be required to prove sufficient funds to support themselves while in the country they are visiting - but this is never in the form of a lump sum shown at the time of travel or at the time of an interview for a visa! Accepted proof of one's ability to support oneself is generally in the form of pay stubs, bank account history (not just a recent deposit of a large sum), and/or in some cases an "affidavit of support" from the inviting side.
If the person who will be traveling is someone known in person to you then perhaps this affidavit of support is what is being requested. In this case you would not actually be wiring funds - you would be submitting a notarized statement that you will be this person's means of support while he or she is in this country.
But in the event that you have already wired somebody a lump sum for an FTA or BTA, and/or if you have provided personal identification of any sort, you should report this to local law enforcement, and to the applicable entity for reporting internet crimes in your region - because it is very likely that this is a scam.
Your best course of action if this is indeed a scam will be to cease all communication with these scammers immediately. If you are located in the US, you can also contact the Internet Crime Complaint Center: http://www.ic3.gov/default.aspx
to report the scam. If you have already sent any funds you should also report the scam to your local law enforcement officials.
As for the type of visa required for someone traveling from the UK to the US for the purpose of marriage: this is a K-1 "Fiancee Visa"
I hope that this information is helpful, and if so that you will please click the green "ACCEPT" icon as this is the only way that I can be paid for my answer through JustAnswer.
Edited by M.Arch on 7/5/2010 at 9:27 PM EST