Manners was Mentioned in Despatches and awarded the DSC for gallantry, determination and skill: postwar analysis showed that he had indeed sunk U-1274. On the same page of the London Gazette his brother, Errol Manners, was also awarded the DSC, for outstanding, courage, tenacity and devotion to duty when his ship Bedouin was sunk defending a convoy to Malta.
Manners’s father, called from retirement to be a convoy commodore, led 52 convoys, and was knighted and Mentioned in Despatches, while another son and a daughter were officers in the Navy.
John Errol Manners, descended from the 2nd Duke of Rutland, was born in Exeter on September 5 1914: his father, Admiral Sir Errol Manners, was a naval officer and a distinguished theologian [his mother an Australian]. Aged 13, young Manners followed his father into the Navy.
Aged 103 he took part in a television show, 100 Year Old Driving School, though soon after he restricted himself to driving his mobility scooter to the local shop.
His wife [Mary nee Downes] predeceased him in 1995. They had two daughters, one of whom was christened in the ship’s bell of the Eglinton, and a son.
John Manners, born September 25 1914, died March 7 2020
It would appear that Lt Cdr Manners was descended from Lord William Manners, the second son of the second Duke of Rutland. Lord William never married, so it is unsurprising that his descendants do not appear in Debrett's or Burke's Peerages. While one cannot unquestioningly accept everything in wikipedia, the article on Lord William at https://en.wikipedia.org/wiki/Lord_William_Manners states that the youngest of his ten children by his mistress, Corbetta Smyth, was Robert Manners (1743-18 April 1810), who married Elizabeth White (1749-1817), and had numerous descendants including Rear Admiral Sir Errol Manners (1883-1953).
I have not been able to verify all that follows, but, piecing together information from the internet, it appears that the above-mentioned Robert Manners and his wife Elizabeth had eleven children (see https://www.genealogy.com/forum/surnames/topics/manners/303/), the ninth of whom was Lt Col Henry Herbert Manners (1786-1843), who married Sabina Poole Brissett (c.1791-1874) on 24 April 1813. They had six sons (and four daughters), including Col Herbert Russell Manners (1819-1907), who married Angela Brown and had a son, Herbert Alexander Erskine Manners (1855-1938), who married Emma Phoebe Evatt (1856-1929), and had issue, including Rear Admiral Sir Errol Manners.