Thank you. A fiduciary broker simply means a professional advisor or body licenced to transact specific otherwise regulated transactions. In Englad we tend to refer to them as credit, mortgage or stockbrokers and of course every major bank offers all these services and can therefore be described as such. All your UK bank appears to be asking for is your US banks SWIFT code.
The process of transferring funds to your US account should be fairly straightforward. Your US bank should be able to provide you with its SWIFT code. A SWIFT code is simply a form of routing number which enables international banks to identify which overseas bank it is sending money to.
Providing your US bank is a member of SWIFT (almost all mainstream banks are) it will be able to provide you with its SWIFT routing code and bank number for funds transfer. It is then simply a case of providing that information to your UK bank for them to arrange the transfer and to confirm whether you wish your UK bank to carry out the conversion to dollars or whether you wish your receiving bank to carry out the conversion.
There is or certainly should be no need for any third party involvement. If your US bank does not hold a SWIFT code it may not be able to accept international payments. If this is the issue you will need to consider appointing a currency broker intermediary to receive and convert the funds from your UK bank and then transfer them in dollars to your US bank.
If this is what you require there are many such brokers you can consider using and they can typically offer better conversion rates than major banks. It is essential you confirm that any broker you consider is registered with the Financial Conduct Authority however. A couple of examples of leading brokers are as follows but these do not serve as recommendations and it is important to do your own due diligence before appointint one:
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