Thanks to all of you for the feedback,
I have done various further bits of digging on the internet, and based on that;
The headbadge OldTel thought the micrometer design was pre-war,however I have found via http://sports.groups.yahoo.com/group/Bi ... ssage/6368
a similar headbadge on a Dayton of the 1940s, and the Dayton catalogue of 1954 and other restorations of bikes of the 50s show the micrometer design
OldTel suggests the spur on the dropouts suggests the 40s
OldTel also supplied the page from the 1948 catalogue which KeithGlos thought showed a 51 model, but having seen the full catalogue the page before (see attachment) does say the lugged version was for 26" wheels (not 27" as the amalgam frame) and was built from double butted 531.
These to me suggest it is genuine and probably pre 1950, my research into trademarks hasn't helped date the headbadge. However there was a seattube decal and the trademark search shows that in 1942 Dayton registered a logo with the micrometer D design with the word cycles beneath it, but in 1947 they registered an almost identical one with the word Dayton replacing cycles, however on the 1948 catalogue they used the older design on the cover
Next task look through very old photos to see if I took any pre repaint pictures