Trenerth began his apprenticeship to William Butte, a member of the Mercers’ Company of London, in 1402. Five years later he paid a fine of £3 6s.8d. to become a freeman of the Company, and between 1411 and 1414, having ended his apprenticeship, he proffered the normal livery fee of £1 (in the customary three instalments). In 1416-17 his fellow mercers fined him 3s.4d. because ‘il dona son chaperon [hood] deynz deux ans passez encontre lordynaunce’. Meanwhile, he had diversified his trading interests by establishing links with the tin miners of his native Cornwall. For several months from November 1406 he was suing one John Breagha in London for detinue of 1,000 lbs. of white tin, not coined; and in June 1409 he brought a large consignment of some 11,000 lbs. to be assessed in the coinage hall at Lostwithiel. No doubt his marriage to the widow of a London pewterer enabled him to expand this side of his business. His Cornish connexions are also revealed in 1418 when, described as ‘citizen of London’, he went surety at the Exchequer for Sir Hugh Courtenay and Thomas Archdeacon, who were then taking custody of lands in the West Country during the minority of the Fitzwaryn heir and it was also as ‘citizen and mercer of London’ that he later brought a suit against a Cornish gentleman for a debt of £2.
Although Trenerth retained small landed holdings in Cornwall (in Tremoderet and Roche),
