Hi, The first mark(??& Co.) is the maker's trademark. The second two (NS) signify that the item is made from Nickel Silver (has no silver content). The third (EP) indicates the nickel silver has been Electroplated. The fourth (crossed keys) just fancies it up. Most likely of British origin.
This famous company of cutlers began life as producers of Sheffield Plate in 1828 and were the second Sheffield firm to receive a licence to begin electroplating in 1843. They went into liquidation in 1892 and were acquired by Walker & Hall."