I myself am looking into the Knotts at Cleobury Mortimer my Great Great Grandfather James Mayne Knott(Born 1844) had a brother called Henry Mayne Knott (one of 7 children including Harriet M Knott/Thomas M Knott/Sarah M Knott/John M Knott/and a Richard Mayne Knott named after his father and grandfather!)Richard Mayne Knott their father was born in 1814 and married to Caroline Marie. Therefore this is to early for your date of 1818.
However Richard Mayne Knott (born 1814) had many other siblings but I only know about his brother John, and I also know about his father called Richard(just to make it easy!) Knott(Born 1789) It is possible that the Henry Knott you are looking for was one of the other children of this Richard Knott who married Evelyn Mayne in 1813.
Richard Knott's father was a Farmer and a Cooper born 1762 and that is where my records stop.Whilst Evelyn was the only daughter of Sir William Mayne and Lady Evelyn, Evelyn Mayne (the daughter) had a brother who went on to become a senior figure under Peel in the early Police Force -Sir Richard Mayne).