In 1308 he was chosen as one of the Barons of the new
Court of Exchequer (Ireland); he was given the title of Chief Baron in 1309, but stepped down from office in 1311.
Corruption He served three terms as Lord Treasurer between 1314 and 1325. During the
Scottish Invasion of Ireland 1315-18 he was the official principally charged with raising funds for the defence of Dublin. He was ordered to reside in Dublin Castle and ensure that its defences were adequate. He was also ordered to cooperate fully with
John Hotham, the former
Chancellor of the Exchequer of Ireland and future
Bishop of Ely, who had returned to Ireland and been given wide-ranging powers of government for the duration of the crisis: effectively Hotham was Governor of Ireland. In 1325 he attended a seemingly routine Exchequer
audit in
London, where grave irregularities in the
Exchequer of Ireland came to light. Serious questions were raised about Islip's integrity, and in one of the first examples of an official inquiry in Ireland, a Dublin
jury was selected to determine the truth of the allegations of
fraud and corruption against him.
Alexander de Bicknor, the Archbishop of Dublin and
Lord Chancellor of Ireland, was accused of the same offences. Islip was finally removed from office as Treasurer: he was imprisoned for a time in the
Fleet Prison, and his goods were seized. Bicknor, despite his archepiscopal rank, suffered the same punishment. In 1334 Walter was ordered to repay the Crown the then-considerable sum of £1332, and in default of repayment, most of his Irish lands were
forfeited. In 1336 he obtained a
royal pardon for all his faults and transgressions; at an unknown date he also obtained a reversal of the excommunication pronounced against him in 1329. Bicknor also received a pardon, despite his previous unsuccessful attempt to
forge one.
Last years He held office as
Custos rotulorum for
Kilkenny. In 1339 he
rented out a number of houses to the Exchequer as temporary accommodation for its offices It is possible that he returned to Kilmainham Priory to spend his final years.
John de Grauntsete In 1329 he was engaged in litigation in the Court of the
Justiciar over the possession of lands with one William de London; the striking feature of the case was that de London was represented by one of Islip's colleagues on the Bench,
John de Grauntsete. Such conduct seems to have been unheard of even at the time: Cohen calls it "startling", and without parallel in legal history. Grauntsete's conduct is even more striking since he was apparently the
tenant of the land in question himself. De Grauntsete was soon afterwards removed from the Bench for a time: the reason for this was apparently not his conduct in Court, but the fact that he had read out letters of
excommunication directed to Islip from the Pope, thus allegedly subverting the Royal authority. ==Kilkenny Witch Trials==