Just to wrap this up, the eBay seller goes by the name "ClubSoulSaver". In the auction that I won (not bad...GBP87) he wrote:
ORIGINALITY:
THESE BUTTONS WERE PRODUCED AT LUCAS FOREMANS ROAD 'PLASTICS' SITE FOR USE IN HORN PUSHES ASSEMBLED AT ANOTHER LUCAS BIRMINGHAM SITE, GREAT KING STREET
NEW OLD STOCK, CAME DIRECTLY FROM THE GT KING ST R7 ASSEMBLY STORES TO ME IN 1986 WHEN LUCAS WERE CLOSING THE SITE AND DISPOSING OF ALL OBSOLETE TOOLS AND STOCK. I WORKED THERE UP UNTIL IT CLOSED- SO I CAN GUARANTEE IT IS AUTHENTIC.
SINCE 1986 HAS BEEN STORED BY ME, CAREFULLY WRAPPED, UNDER COVER, OUT OF THE LIGHT.
THESE ARE AS NEAR TO PERFECT AS LUCAS QUALITY & PROCESS THEN ALLOWED. THERE IS NO SIGN OF FADE, AND NO CRAZING.
I HAVE BEEN ASKED IF I WOULD BE PREPARED TO CERTIFY THEIR AUTHENTICITY AND ORIGINALITY: IF THE WINNING BIDDER REQUESTS A WRITTEN STATEMENT OF AUTHENTICITY I WILL HAPPILY PROVIDE SUCH AN ENDORSEMENT.
The horn button I was shipped was safely packaged in a sweet (candy) tin & is a thing of beauty.