I found an old ten gauge a little while ago, I'd like to check it out.
What I know so far is that it is an English gun, the markings are J. Manton, London, Laminated Steel, this is not the Belgian knock off (learned this from proof markings and also all references I've seen to this are marked "J. Manton & Co."), at this point I have no clue of an approximate year nor do I know what it is worth (mainly just curious on this one). The barrels are 31 7.8" long.
Just for emphasis this gun is
NOT marked J. Manton & Co. anywhere.
Here are photos, click on each one to see a larger version.
Side, complete:

Top, complete:

Side plate marking:

Top marking (between barrels):

Stock checkering:

Chambers:

Firing Pins:

Sight Bead:

The Crest:

I took it apart and did not find any more marking other than the British black powder proof markings on the underside of the barrel.
Thanks,
Sequoia