Tim, much of what you seek is in the archive already -- a pleasant way to learn stuff you didn't know you wanted to know, while also finding what you seek.
To repost, briefly, some info I posted in February of this year, "Following up on a thread from a few weeks back, I finally did speak this week with Barry Witcomb at Witcomb Cycles in south London. As had been guessed, the last two digits of a serial number are the year of construction and the rest of the number is sequential, based on the order the frames are completed. He's got good records back to about 1962. The frames were built in-house from about 1959 or 1960 so there's spottier records for the frames before 1962."
So your 1018873 was built in 1973, not long after Witcomb completed its ten-thousandth frame. If yours was originally a custom build, a call to Witcomb may reveal who built it. You may also be able to order a decal set.
Barry/Barrie (he's used both spellings, but the "ie" is the current spelling, I understand) is still building and repairing frames. I was going to order a decal set from him, but I'm now convinced that the Witcomb I've got has had a front-ender. That has me thinking about the uneconomical but emotionally satisfying possibility of taking/sending the frame to Witcomb for respray plus any tweaking needed.