[9] John Periam in 1720 built a mansion at Sandhill Park in the parish of Bishops Lydeard, Somerset, which descended to the Lethbridge family.

Periam was descended from Sir William Peryam (1534–1604) of Little Fulford, near Crediton in Devon, Lord Chief Baron of the Exchequer under Queen Elizabeth I.

However, it seems this gift was later used as a reason for the king to compensate the 1st Baronet by the grant of the title "Baron FitzWarin", alias "Fitzwarren".

In 1809 he made an application to the king for the barony, and in 1811 his son wrote to the Prime Minister that this had been desired by his father "for many years", "as a mark of royal favour".

He served as Member of Parliament for Minehead in Somerset from 1806 to 1807, apparently due to the influence over that seat exerted by his friend John Fownes Luttrell (1752–1816), feudal barony of Dunster of nearby Dunster Castle, who "having incurred liability for a treating offence [a form of electoral fraud] and to avoid risking a petition, returned Lethbridge as locum tenens until the danger of a petition was past".

It appears that Lethbridge had an affair with Mary Jane Vial Clairmont, who gave birth to a daughter on 27 April 1798 in Brislington, near Bristol.

When the younger of these, Mary, eloped with the poet Percy Bysshe Shelley, Claire Clairmont accompanied them on their flight to Europe.