Within an oval on the steerer tube, there are four lines stamped as follows:A & P
BGT
G13A...
B...
I'm not certain about the "A" after G13, and the ellipses (...) indicate that there are additional characters that are too faint to read.Interpreted From Classic Lightweights UK site information:
"A&P" means the steering tube was Accles & Pollock tubing. "BGT" should be "BST" for British standard thread. "G13A..." could be "G/13/16" which equals "...Gauge (wall thickness is 13-standard wire gauge one end and 16 the other = 2.3mm thick at the crown and 1.6mm thick at the top, threaded end (as all modern steerers)." B.. should be "BQ" means "B" quality tubing.