Hey that Rudge has almost got an STI on the right!
Seriously though I had a Coventry Eagle that was very similar in most respects and that was, according to the seller who had owned it from new, from about 1970. Much of the British bike industry was very conservative and features stuck around for a long time, stocks of things like lugs could last an age. Hell, some are still cropping up NOS now. Touring bikes in particular hardly changed for years, although a tourer would have been more likely to come with a three speed hub than derailleur gears.
Add to that the fact that it's very likely that Edwardes built this up around a bought in frameset and who knows how it ended up that spec. It could have been changed over the years, it could have been off the peg like that or it could have been a custom order. They could have had the frame festering in a back room for years before it was built up. It could even have been a custom built frameset, unlikely but possible. They could have refurbed a customer's existing bike.
All this is why dating bikes like this is next to impossible without any provenance.
Whatever it is it's nice to have something like that.