Johnston commissioned just before start of war and introduced in 1916.

Not a commercial font of course.

http://new.myfonts.com/search/release_date%3A1916*/fonts/

Thanks, i guess i should have mentioned that i am basing a project on Johnston's typeface, and i wanted to see what other typefaces were being designed at the same time he done his for the Underground.

You could start from here, maybe.
http://new.myfonts.com/search/tag%3A1910s/fonts/

On the American side of the Atlantic, Frederic Goudy was several years into his late-starting career as a type designer. According to Wikipedia, Goudy Old Style was released in 1915.

http://en.wikipedia.org/wiki/Frederic_Goudy

I'm assuming that much of the Underground signage would have been hand lettered, not produced from type.
I wonder to what extent that informs the shapes of the letters in this early example of comprehensive, controlled branding.
It might be worth investigating manuals of sign-writing/lettering/trade cards from the same era.
This from 1933. Note the two "S"s in the title, different, but both constructed from arcs of circle.

Thanks for all your suggestions, I will definitely try and find some other examples of sign-writing/lettering, and thank you for the image you posted Nick Shinn, interesting point about the difference in the 'S's.

Luke if you can get down to St Bride in London they have (IIRC) lots of source material for Johnston (and Gill, who was briefly a part of the Johnston project).

Thats good to know, i did go there the other month, but was before i had settled on a subject if i can afford to ill try and go up again after Christmas. I have contacted Crafts Study Centre in Farnham asking if it would be possible to view their collection of his work, as it is closer, but still waiting on a reply.

Nick Shinn, I've noticed that some of the Victoria line platform signs at King's Cross still use that particular S. I managed to do a rubbing as the lettering is ever so slightly raised - there are bones in the middle of the S - it is indeed two arcs. Perhaps the whole sign wasn't Johnston per se, but I wasn't able to tell the difference at the time. Only at King's Cross though…

I'd upload the rubbing but unfortunately can't find it.

You can search Seemann’s »Handbuch der Schriftarten«, the largest German typeface compendium from around that time here:
http://www.global-type.org/Searching.743.0.html
(Some with pictures—the word Hamburg—others info only.)