Ralph’s kinsmen, Michael Trenewith and his son Ralph, represented Cornwall in the Parliaments of 1338 and 1352, respectively. The career of the former affords a typical example of the malversation which flourished in the stannaries at that time: his lawful business operations included ownership of tin mines and loaning money; his criminal activities included smuggling, wrecking, fraud and coercion. But it would seem that Ralph, the MP for Truro, may be likened to Michael only in his more legitimate dealings: thus, from the 1360s onwards he traded in large quantities of tin which he took to be smelted and coined at Lostwithiel. (On one occasion, in 1385, he brought to be assayed a consignment weighing as much as 12,400 lbs.)
Trenewith was a landowner of some substance. By a settlement made in 1359 he came into land on the manor of ‘Trenewith and Trewyshanec’ (probably in the parish of St. Probus), and six years later he was possessed of extensive properties near Looe. His holdings included land at Ventonwyn and Tresawle, situated near Truro, the borough which he represented in Parliament. Trenewith’s second marriage, which may have taken place before 1373, when he had dealings with his wife’s father, allied him to one of the most important families in Cornwall. By 1386 he had produced four children by this marriage who, under settlements made by their maternal grandfather, Otto Bodrugan, stood to inherit nearly all of the Bodrugan estates. Small wonder that the eventual heir, William renewith (Ralph’s only surviving son by this marriage), changed his name to Bodrugan.
It was no doubt Trenewith’s interest in the tin trade which brought him into contact with the administration of the duchy of Cornwall. He was made responsible for the purchase and sale of tin to the use of Edward, the Black Prince, in about 1367, and became receiver of the prince’s estates in Cornwall two years later. As such in June 1376 he was commissioned to conduct an assession court, and he then took the opportunity of extending a lease of the Fal estuary, which he had been holding since the previous accession. Later on he also held a lease of the cellars beneath the great hall of the duchy in Lostwithiel, which, however, was to expire before 1391.
Trenewith is recorded on various occasions after the end of his receivership: in 1383 he acted as mainpernor at the Exchequer for the prior of St. Michael’s Mount; in 1388 he put in claims to certain of the properties forfeited by the chief justice, Sir Robert Tresilian; and in 1389 he stood surety at the Exchequer for a lessee of other parts of the Tresilian estates. In February 1392 he himself was granted custody of lands in Cornwall which had belonged to John Durant, during the minority of the latter’s son John, together with his marriage, for which he paid £20. Consignments of tin were still being brought to Lostwithiel to be coined in his name in September that year, and there can be little doubt that it was indeed he who was returned for Truro to the Parliament which met the following January.