In 1983* (while I was at university in Sheffield) I saw this book in a secondhand store but didn't have enough spare cash to buy it. It was an occult conspiracy thriller but written in part as a pastiche of Sax Rohmer's Fu-Manchu books. It involved the Spear of Longinus and may have had 'Golden', 'Spear' or 'Golden Spear' in the title.
At the time (80s) it seemed a fairly new printing and it was in standard paperback.
*It was definitely 1983 as Terry Pratchett's first discworld book was just out.
Positively identified below as Richard Jaccomo's The Yellow Peril. Amazon.co.uk confirms there was a 1980 edition which would have been the one I saw. A (disparaging) review on Amazon also confirms that the Spear of Destiny appears in the novel.