It's always good to see a returning Guardian, particularly when they come bearing treasure like that!

Nice find

It's a great-looking Lambsfoot, covers are certainly bone, strange to see such an off-centre blade though
John Nowill & Sons have history going back to !700 when one their 2 longstanding marks (* over D) was granted to Thomas Nowill (1676-1704). The mark subsequently passed to his younger brother, William, and then to his son David. In 1786, David's son, Thomas Nowill, co-founded Hague & Nowill, a partnership which lasted until 1797. After Thomas Hague retired, the business became Thomas Nowill & Co, and in 1811, Thomas Nowill & Son, employing between ten and thirty men.
In 1825, Thomas retired himself, and his sons Thomas and William worked together, manufacturing silver fruit & dessert knives, penknives, pocketknives, fancy knives, and desk knives, along with various other items. Following their father's death though, they went their separate ways, each running their own cutlery business.
In 1842, John Nowill acquired the 'Krosskeys' mark. He died in 1847, leaving 8 sons, (with 5 joining the business). The youngest, Arthur, died in 1896, but the 4 brothers continued to run the business jointly. John, the oldest brother, was the senior partner, and the business continued to expand under his watch, employing a hundred men by 1881, as well as 10 boys, and 15 women. After John's death in 1900, his own sons ran the business, along with their uncle, Jack.
In 1928, Nowill's became a limited company, with Jack's son William Esmond Nowill as the senior partner. In 1947, the business was sold to F.E. & J.R Hopkinson Ltd, which continued to use the Nowill marks. They are still in use by Jack Adams Ltd, who subsequently acquired Hopkinson.
That's bad about the blade, and unusual. I think it would be worth you getting it fixed, not too hard for something with cuttlin' skills I'm told