Denny came from a family of London fishmongers of comparatively modest means. He may have been of age by July 1375 when named as co-executor with his stepmother of his father’s will and as heir to certain properties situated for the most part in the parish of St. Andrew Undershaft. However, it was the deaths of a number of relations on his mother’s side which enabled him to acquire more substantial holdings in the City. Thus, in 1381, the property which had once belonged to his uncle, Walter Waltham, including shops and tenements in the parishes of St. Magnus the Martyr, St. Dionisius Backchurch and All Hallows Staining, came into his possession, while in 1396 and 1397 he acquired even more of the estate built up long before by his maternal grandfather, Hugh Waltham, sometime town clerk of London, situated in the parishes of St. James Garlickhithe and St. Katherine. Certain of Denny’s tenements were held on leases from St. Mary Graces abbey or from the priory of St. John Baptist, Haliwell, and he himself rented them out to sub-tenants. A dispute with one of the latter, a chandler named Thomas Beaumond, over the annual payment of a pottle of oil and a bushel of peas, was to come before the court of the mayor and aldermen in 1414, judgement being given in the landlord’s favour. Two years earlier the income which Denny derived from his city holdings had been estimated at £24 4s.7½d. a year, for the purposes of taxation.
Denny’s marriage to the widow of a country gentleman enabled him to break away from the family background in trade and himself join the ranks of landed knights and esquires. Amy Furneaux held for life the Cambridgeshire manor of Barham as her jointure by settlement made by her former husband, as well as a third part of the manor and advowson of Middle Harling in Norfolk as her dower portion. Denny seems to have taken a personal interest in the Cambridgeshire property only until about 1399; by that date he and his wife had transferred their life tenancy of Barham to John Fordham, bishop of Ely.
Indeed, Denny’s quarrel with the Clipstons of Bartlow very nearly landed him in serious trouble with Richard II’s council during the months of political crisis in 1397. It all began quite innocuously in September when Sir Robert was appointed to royal commissions to arrest William and Thomas Clipston and their accomplice, John Faunesson, ‘clerk of the Wolde’, and to find by local inquiry the whereabouts of their goods and chattels, which were then to be confiscated. But the zeal with which he carried out the charge, threatening the lives of the accused men ‘pour auncien ire et malice quil a eux avoit’ and wantonly destroying some of their property, allegedly led to ‘insurrections and unlawful confederacies’ in both Cambridgeshire and Essex. The outraged William Clipston and his followers presented a number of bills against Denny before the King, and in November none other than Richard’s trusted councillor, Sir John Bussy, was appointed to investigate the affair. In the event Bussy discovered no evidence of rioting, and even though Denny’s culpability on other counts as alleged in the bills was found proven, he was nevertheless named on another commission set up a month later to seize the Clipstons’ possessions. It was doubtless as a response to these local troubles, rather than because his loyalty to King Richard was suspect, that Denny saw fit to purchase a royal pardon in June 1398. His feud with William Clipston was by no means at an end: in 1404 he was to bring a suit against the 12 members of the jury which had given a verdict for Clipston in a cause of trespass heard in the King’s bench, alleging that they had taken bribes from his opponent; and three years later his son, Thomas, was to lay in ambush for Clipston and kill him by striking him on the head with his sword. (The young man obtained a pardon in 1409.)
Denny had continued his association with the duke of York’s retainers, Sir Thomas Gerberge and Sir Thomas Genney: all three provided securities in May 1398 on behalf of certain men required to appear before the Council, and two months later Denny and Gerberge appeared together as mainpernors in Chancery for a man from Surrey being sued by the prior of Bermondsey. From that time onwards Denny gradually switched his interests to the south-east, and came to be increasingly associated with men of those parts, such as Sir William Burcester (for whom he stood surety in 1400). Thus, in 1401 he offered support to two chaplains engaged in a dispute with the master of the hospital of St. Thomas the Martyr in Southwark, and in later years he was occasionally described as being ‘of Surrey’.
In 1417, towards the end of his life, Denny made a quitclaim to St. Mary Graces abbey of his title to a messuage and 12 shops in the London parishes of St. Andrew Hubbard and St. Mary at Hill, near Billingsgate. It was in the church of St. Andrew Undershaft that he requested burial in his will made on 28 Oct. 1419, and in the same document he stipulated that his widow, Amy, was to have possession of his property in four city parishes for term of her life, on condition that she supported a chaplain to pray for his soul. He named as Amy’s co-executors Sir William Bardwell and Richard Osbarn, citizen of London. Probate was granted in the commissary court of London on 7 Nov. Amy Denny’s will, made four years later on 23 Sept. 1423, contained a bequest to her son, Thomas, of a primer embossed with an escutcheon of the Denny arms.