It is important to distinguish what letter follows "18ct" as it may indicate that the piece is plate, gold plate, gold based, etc. The 18ct mark alone says that the piece is an alloy, a mix of several metals with around 70% gold.
The description of the "BB" mark alone is not enough to advise you of the maker as the initials B.B. are very common. If possible, it would help to see a close-up photo of the aforementioned mark. I hope this helps some.
