Largely from the sale of the family library, in the summer of 1877 he purchased Woburn Park, home of the wealthy Southcote family, 100–120 acres (0.40–0.49 km2) of mostly deer park-style landscape fronting briefly the River Thames, in Addlestone, Surrey, England and containing a commanding knoll above the end of the combined Bourne, a deep stream and its confluence.
Lord Petre, wearing sumptuous robes, acted as Speaker as the boys, sitting as members for imaginary constituencies such as Chilcompton, Gurney Slade and Radstock, debated "bills" in precise imitation of the House of Commons.
The accidental death by drowning of Fotheringham, a senior boy staying at the site in the holidays, dented the confidence of prospective parents.
...It has been a touching and a noble sight to see the heir to an old Catholic peerage throw aside all purely worldly and vain attractions and devote the best years of his life to the work of an educational reform, generously and sympathetically building up and courageously striking out on behalf of his ideal.
Petre has done no more than emphasise the necessity of preparing Catholic youth to take part in the public life of the country, he deserves our lasting gratitude.
... Those who have grown up within its walls, and those who are still within them, bear ample and decided testimony to the punctuality, exactness, and even punctiliousness of its discipline..."[citation needed] Five weeks later, on 4 July 1884, William's father died and he succeeded to the title as 13th Baron Petre of Writtle.
Lord Petre then retired to The Hyde in Ingatestone, Essex; also, in 1885 the Duchy of Lancaster granted him the Liberty of Clare and the Manor of Arnolds.
Eight years later, he died at the early age of 46, his health apparently undermined by the strain of attempting to establish a new type of education for Catholic youth.