Rifle’s barrel set measures 26”, shotgun’s measures 28”. Both have bright chambers and bores. Crisp rifling on a .406 bore. I can’t tell by the stamping if we have a 55 gr cordite proof or a 60 gr , being an Indian market rifle I would guess 55 gr cordite. With my aging eye balls and old Kynoch, the rifle printed a nice 1 1/4” group at 55 yards (see picture).
The 20 Ga 2 3/4”is Birmingham proofed post 1954.
Both sets of barrels have good soldering, 99+ % blacking and are tight on faces of breech. The shotgun configuration balances right behind the hinge pin. The shotgun weighs 7# 14 oz, the rifle weighs 10# 9oz.
The action is in great mechanical condition with good trigger pulls and strong ejectors. Deep chiseled acanthus leaves engraving with 90 % plus coverage. I’m guessing the gun was refinished in England at the time the shotgun barrels were fitted and had a most sheltered life since.
The stock LOP is 14 1/2” over a 1” Silvers pad . I cannot find any reference about the coat of arm on the cheek piece medallion. The number 2 could be an armory number.
However, judging by the engraving and the walnut quality, the gentleman who special ordered the rifle was a man of taste.
The wood finish and checkering are in excellent condition, not oil soaked and very strong.
Comes in a Beretta canvas case.
Joseph Manton was the forefather of the modern English gun trade and his work not only advanced the technology of firearms but also influenced a generation of gunmakers. Notable figures such as James Purdey, Thomas Boss, William Greener and Charles Lancaster (to name a few) trained under him, contributing to the evolution of the gun trade in London.

More pictures can be seen on Guns International by following the link below:

https://www.gunsinternational.com/guns-for-sale-online/rifles/double-rifles-english/manton-400-ex-or-450-400-3-1-4-ejectors-with-extra-barrels-in-20-ga-.cfm?gun_id=103543047&cdn_bp=1