Thomas Pitt of Boconnoc
He was Assay master of the Stannaries from March 1738 to February 1742 and Lord Warden of the Stannaries from February 1742 to March 1751, when the Cornish Stannary Parliament met for the last time.
As head of the family, Pitt inherited both his grandfather's immense fortune and his parliamentary boroughs - he had the complete power to nominate both MPs at Old Sarum and one of the two at Okehampton, as well as considerable influence in at least two Cornish boroughs, Camelford and Grampound. He had himself elected Member of Parliament for Okehampton in 1727, the first election after he came of age, and represented the borough until 1754; but on a number of occasions he was also elected for Old Sarum, which meant that when he chose to sit for Okehampton the Old Sarum seat was free to offer at a by-election to somebody else who had failed to get into Parliament.
Pitt was ambitious for political influence and, attaching himself to the retinue of Frederick, Prince of Wales, managed the general elections of 1741 and 1747 in Cornwall in the Prince's interests; but this involved massive expenditure - especially at the notoriously-corrupt Grampound, where he spent huge sums both on bribing the voters and on lawsuits attempting to deprive the most rapacious of their votes.
By 1751 Pitt had bankrupted himself, and the death that year of the Prince of Wales destroyed his hopes of securing influence or patronage for his efforts. He mortgaged his boroughs to the Treasury, allowing the government to name two MPs at Old Sarum and one at Okehampton in return for a pension of £1000 a year. After sitting briefly for Old Sarum in the 1754 Parliament, he resigned his seat and fled the country.
Returning to England in 1761, however, Pitt persuaded the government to allow him to be once more elected for Old Sarum - a temporary measure, he promised, to prevent his being arrested for debt until he was able satisfy his creditors. (MPs were immune from civil arrest.) He promised to relinquish the seat at the earliest possible moment and allow the government to name his replacement in accordance with the original arrangement; but he died a few months later, still MP for Old Sarum.
He had married the sister of Lord Lyttelton and was the father of the first Baron Camelford, who repudiated his father's arrangement for Old Sarum, and chose himself as MP when he inherited the borough.
- Robert Beatson, A Chronological Register of Both Houses of Parliament (London: Longman, Hurst, Res & Orme, 1807) 
- Lewis Namier, The Structure of Politics at the Accession of George III (2nd edition - London: St Martin's Press, 1961)
- Leigh Rayment's Historical List of MPs [self-published source][better source needed]