Much like other comments point out - Broken Sword borrowed liberally from the same "Holy Blood, Holy Grail" book material that Dan Brown also took. Broken Sword even includes an informant character called "Plantard" - surely a reference to Pierre Plantard etc.
It's undoubtedly the common ancestor in HBHG that lead to Broken Sword and The Da Vinci Code having very similar plots and ideas - HBHG sold reasonably well, I don't buy into the idea Dan Brown needed to play Broken Sword to write the book - HBHG came out in 1982. There are many other trash-pseudo history books on the knights templar that allege conspiracy/cults etc pre-dating Broken Sword - as a kid I had an insatiable appetite for these books too.
Charles Cecil (driving force behind Broken Sword) has happily alluded to his own HBHG inspiration in interviews.
It's undoubtedly the common ancestor in HBHG that lead to Broken Sword and The Da Vinci Code having very similar plots and ideas - HBHG sold reasonably well, I don't buy into the idea Dan Brown needed to play Broken Sword to write the book - HBHG came out in 1982. There are many other trash-pseudo history books on the knights templar that allege conspiracy/cults etc pre-dating Broken Sword - as a kid I had an insatiable appetite for these books too.
Charles Cecil (driving force behind Broken Sword) has happily alluded to his own HBHG inspiration in interviews.