The manor of Thetford belonged to the duchy of Lancaster and was administered by a bailiff, sometimes called a steward, and a deputy steward. In July 1548 Edward VI leased the ‘dominion and manor’ to the Protector Somerset, and not long afterwards the remainder of the duchy property there to Richard Fulmerston. The priory was dissolved in 1540 over the objection of the 3rd Duke of Norfolk, who was founder’s kin. After Norfolk had received in compensation the priory buildings and the manors of Halwick and Northwick in the town, he leased the priory to Fulmerston, who also acquired the nunnery, canonry and two friaries there. On the duke’s attainder his house and property were granted to the Protector, who alienated them to Fulmerston, but on Norfolk’s restoration they reverted to the duke.3

The town authorities consisted of the mayor, who was sworn in by the deputy steward for the duchy, a common council and a congregation. No municipal records survive for the period. The borough was presumably enfranchised at the suit of the chancellor of the duchy, perhaps with the support of the Duke of Norfolk. It is not on the list of constituencies drawn up in connexion with the issue of writs de expensis for the Parliament of 1512, but it appears at the end of the list of Members of the Parliament of 1529, preceded by two other duchy boroughs, Lancaster and Preston. Like Lancaster, it could have returned in 1523, or even in 1515, but the probability is that Giles Heron and William Dauntesey were its first Members. Both Heron and Dauntesey were sons-in-law of Sir Thomas More, who was chancellor of the duchy at the time of the elections of 1529. After the delivery of a precept from the sheriff of Norfolk and Suffolk the elections were held under the direction of the mayor in the common hall. Indentures survive for all the Parliaments between 1547 and 1558, except that of November 1554. They are in Latin and the contracting parties are the sheriff and the mayor and burgesses. They record that the mayor, burgesses and others of the common council and congregation have elected the Members ‘with one voice’.4

The influence of the duchy on the Membership after 1529 was limited. In 1547 John Brende, a soldier known to both the Protector and Sir William Paget, and Richard Heydon, a Norfolk lawyer employed as a feoffee by Sir Thomas Paston, probably owed their election to the duchy, of which Paget was then chancellor and Paston the steward in Norfolk, Suffolk and Cambridgeshire; the intermediary could well have been Fulmerston, who was or was about to become a member of the Protector’s household and who later came to dominate the patronage. Sir John Clere was a lifelong friend of Fulmerston, his son Edward married Fulmerston’s daughter and one of his sons-in-law was Walter Haddon. The Cleres and several of the other Members were related to the dukes of Norfolk, to whose service Fulmerston returned in the 155os, and Robert Barker was perhaps a relative of the 4th Duke’s secretary William Barker. Henry Northey, chosen with Sir John Clere early in 1553, was a servant of the 2nd Earl of Sussex, whose son Sir Thomas Radcliffe was elected to the same Parliament as one of the knights of the shire. Robert Drury was a son of Queen Mary’s Councillor (Sir) William Drury, who owned property in the locality, but he was also connected with Sir Robert Rochester, the chancellor at the time of his return. Nicholas Rookwood, chief prothonotary of the common pleas, lived four miles away at Euston in Suffolk and his local standing probably explains his return.

By an Act of 1534 (26 Hen. VIII, c.14) Thetford became the seat of a suffragan bishop until early in Elizabeth’s reign.