I trust the OP is aware these square corner safes have no security or fire protection value - there is a Chubbsafes vid somewhere on youtube of a holdfast safe being cut apart in a minute with an anglegrinder.

Some old safes were dark green, I've also seen Milners in maroon.
I've seen this sort of drop handle on old bookroom doors, so though it does not look right for a safe it could be a replacement supplied by Milner.

Spruced-up old safes make interesting drinks cabinets.

John Holden Security in its new ownership supplies bespoke safes and can probably do a good restoration job if the OP thinks it worth spending good money.