His regiment was ordered home in 1822, and Thompson saw no further active service; but in 1827 he obtained his majority in the 65th regiment, then quartered in Ireland, and in 1829 he became lieutenant-colonel of infantry, unattached. In 1846 he was gazetted colonel, major-general in 1854, and lieutenant-general in 1860, finally becoming general in 1868, the year before his death.
Almost immediately upon his return to England from India in 1822 Perronet Thompson devoted himself to literature and politics. He entered into familiar intercourse with the circle of ‘philosophical radicals’ surrounding Jeremy Bentham, who was then engaged in providing funds to start the ‘Westminster Review’ as the organ of the utilitarian philosophers. In 1824, then being forty years of age, Thompson commenced a literary career by contributing an article on the ‘Instrument of Exchange’ to the first number of the ‘Review.’ Being prompted by his sympathy with the Greeks, then struggling for independence, Thompson published in 1825 two pamphlets in modern Greek and French on ‘Outposts’ and on a system of telegraphing for service in the field. Coming back to economic subjects, in 1826 he published the ‘True Theory of Rent,’ in support of Adam Smith against Ricardo and others, and his views were approved by Jean-Baptiste Say. In 1827 appeared his most celebrated pamphlet, the ‘Catechism on the Corn Laws,’ which was written in a ‘strong, racy, Saxon style,’ abounding in humorous illustration. This ‘Catechism’—which was described by Sir John Bowring [q. v.] as ‘one of the most masterly and pungent exposures of fallacies’ ever published—purported to be written by a member of the university of Cambridge. It at once obtained wide popularity, no fewer than eighteen editions passing through the press by 1834. An immediate effect of the publication of the ‘Catechism’ was the election of Thompson as a fellow of the Royal Society in 1828. In 1829 he struck upon a new line of literary effort by writing ‘Instructions to my Daughter for playing on the Enharmonic Guitar; being an attempt to effect the execution of correct harmony on principles analogous to those of the ancient Enharmonic’ (his enharmonic organ, constructed in accordance with his theory, was shown at the Great Exhibition of 1851, and ‘honourably mentioned’ in the reports of the juries. It is still to be seen in the South Kensington Museum). Slightly varying his literary work, he next published, in 1830, a mathematical treatise, ‘Geometry without Axioms,’ which he described as an endeavour to get rid of axioms, and particularly to establish the theory of parallel lines without recourse to any principle not founded on previous demonstration. The work went through many editions, but having been well translated by M. van Tenac, professor of mathematics at the royal establishment at Rochefort, received more recognition from students in France than at home.
Meanwhile, in 1829 Thompson became the proprietor of the ‘Westminster Review,’ and for the seven years that he owned it he was the most prolific contributor, writing upwards of a hundred articles. One of these, in support of catholic emancipation, was republished under the title of the ‘Catholic State Waggon,’ forty thousand copies passing into circulation. Thompson transferred the ‘Review’ to Sir William Molesworth [q. v.] in 1836. In 1829 Thompson published a political pamphlet on the ‘Adjustment of the House of Lords,’ of so radical a tendency that Cobbett republished it in his ‘Register.’ Thompson also wrote, at the invitation of Jeremy Bentham, the ‘Notes and Subsidiary Observations on the Tenth Chapter’ (on military establishments) of Bentham's ‘Constitutional Code.’
The reforming zeal of the House of Commons that came into existence in 1832 seems to have inspired Thompson with a desire to enter parliament, and in January 1835 he contested Preston, and received considerable support, although he was not returned. In the following June, however, he was elected for Hull (his native town), but owing to his majority numbering only five votes, he had to submit to a petition, by which, as he expressed it, ‘he was laid down and robbed at the door of the House of Commons’ to the amount of 4,000l. None of the charges preferred in the petition being proved, he took his seat in the house, and added his vote to those of the ‘philosophic radicals,’ chief among whom were Grote, Molesworth, and Warburton, who had already made themselves a name under the directing genius of Bentham. In 1837, however, Thompson was defeated at Maidstone, where he opposed Wyndham Lewis and Disraeli; and although he contested Marylebone, Manchester, and Sunderland as opportunity offered, he did not again win a seat until 1847, when he was elected for Bradford, Yorkshire. In 1852 he failed to keep his seat at Bradford, being beaten by only six votes. Finally, in 1857 he was returned for the same constituency without a contest, but closed his parliamentary career with the dissolution in 1859, not again seeking election.
