Derwent’s antecedents are unknown, but it is a reasonable conjecture that he was the representative of a junior branch of the Derwentwaters of Castlerigg (Cumberland) and Ormside (Westmorland). The main male line of this ancient family failed in the early fifteenth century and the family lands passed to an heiress, the wife of Sir Nicholas Radcliffe* and progenitor of the seventeenth-century earls of Derwentwater. There is no direct evidence to suggest that any of the family estates remained for any surviving male Derwentwaters. It is, however, suggestive that our MP’s earliest appearance in the records is in connexion with property at Colby, only a couple of miles from Ormside: in 1427 he sued a husbandman for illegally harvesting his crops and depasturing his grass there.
Yet, in the early part of his long career, Appleby, which lay near Colby, rather than Carlisle, was the main focus of Derwent’s activities. On 19 Aug. 1430, for example, he sat on a jury when royal justices of gaol delivery made their annual visit to the borough, a task he also discharged in 1434 and 1437 (and much later in his career in 1447 and 1452); and on 16 Apr. 1436 he was a juror in the inquisition post mortem of John Crackenthorpe† of Newbiggin.
In the 1440s Derwent found further promotion in the Household, where he was a yeoman ‘for vesture’.
Soon after, however, as the Nevilles became alienated from the court, Derwent had to choose between two masters, and he followed Neville. He fought in the earl of Salisbury’s retinue at the first battle of St. Albans (or so he later claimed), and was again elected for Carlisle to the Parliament that followed, on this occasion with another Neville man, John Bere III*. On 8 Aug. 1455, eight days after the end of the first session of this Parliament and with Yorkists in control of government, he gained a small mark of favour, namely restoration to the daily wage of 12d. a day that he was said to have lost under the Act of Resumption of 1449 (Nov.). This is curious for he had secured a proviso of exemption from that Act, as he did also in respect of the Act passed during the 1455 Parliament, and one can only assume that his earlier exemption had been disregarded.
When the uneasy truce between the rival factions broke down in the autumn of 1459, Derwent again actively sided with the Nevilles, fighting in the earl’s company at the battle of Blore Heath and taking his place in the Yorkist ranks at Ludford Bridge a few weeks later. According to his own later testimony he was captured there, brought before the King and imprisoned. He was certainly attainted in the Coventry Parliament. On 13 Jan. 1460, Henry Manners was given his post as a serjeant-at-arms, and, two months later, his forestership in Inglewood was granted to the clerk of the King’s signet, John Manfeld. As he had not fled abroad with the Nevilles, however, he was able to save something: on 20 Mar. 1460, ten days after the grant to Manfeld, he sued out a general pardon as ‘Thomas Derwent alias Derwentwater of Carlisle, esquire alias gentleman’. Even so, it is not surprising that he should have reverted to his Neville allegiance on the triumphant return of the Yorkists in the following summer. On his own later account he was in the earl of Salisbury’s ranks at the ‘male iournay’ at Wakefield, when he again suffered as he had after Ludford. He claimed he was imprisoned at Skipton, presumably in the castle of the notoriously violent Lancastrian magnate, John, Lord Clifford, and ransomed for £20. Then, while travelling north to Carlisle, he was captured by Humphrey Dacre (brother of Ralph Dacre*, Lord Dacre), and taken to the Dacre castle of Kirkoswald (near Penrith). Here £22 was stolen from him and he was subjected to daily threats of death because Dacre had discovered, in Derwent’s casket, a pedigree of the descent justifying the Yorkist title to the thrones of England and Scotland.
If this story, successfully presented to the Crown as a plea for exemption from the Act of Resumption of 1467, is accepted as accurate (and there is no reason, beyond the routine exaggeration of supplicants for favour, to doubt its essential truth), it reveals the risks to which the minor functionaries of York and Lancaster were exposed in the civil war of 1459-61. It also shows how little reward some of them derived for their sacrifices. All our MP gained for his troubles was new letters patent, dated 8 Aug. 1461, granting him again 12d. per diem from the issues of Cumberland as a royal serjeant-at-arms. Given the difficulty entailed in securing actual payment of such grants he probably viewed this as scant compensation. In Hilary term 1462 he appeared personally in the Exchequer of pleas and had judgement in £68 against Hugh Lowther* and £23 4s. against (Sir) Thomas Curwen* for their failures as sheriffs of Cumberland in the late 1450s to pay him his fee and its accumulated arrears. It probably did him little good. Curwen, in any event, proved recalcitrant, preventing the shrieval bailiffs from taking livestock in payment in April 1463. Nor did it prove any easier to gain payment in what, from his point of view, were the more favourable conditions of the 1460s. On 14 May 1470 he again presented himself before the barons of the Exchequer, claiming £52 against Sir John Huddlestone†, as sheriff of Cumberland, for the same default. He claimed to have received no payment since November 1466.
Derwent’s poverty and age explain why so little is known of the last years of his life. In August 1466 he was a juror at Carlisle for an inquisition into the forfeited estates of Ralph, Lord Dacre. In 1467 he sued Sir John Pennington* for a debt of £18, probably in connexion with Pennington’s failure, as the sheriff of 1459-60, to pay him the arrears of his daily fee.