Depends on how your are approaching it.

Assuming you have found the vessel, and know what flag it is flying, and if you want to register it through Cardiff. Is the seller a company or private individual and are you sure of the legal ownership. The Cardiff registry will supply what you need, if it is to be taken off a foreign registry. If you do not have a Euro account, you can ask your bank for a banker's draft in the currency of your choice, and this is exchanged at the same time as the Bill of Sale is signed by both parties, including any caveats on both sides.