Thornton, who had seen service with his father’s old regiment in Flanders, Holland and Germany in 1794-5, retired from the army with the rank of lieutenant-general, 29 July 1812.
In June 1814 Thornton resumed his seat for Woodstock on Eden’s succeeding to the title. He gave a general support to administration, but his particular quibbles in debate embarrassed them; nor, apparently, was he popular at Woodstock. In London society he was best known as ‘a popular professor of the waltz’,
Thornton supported government measures in the session of 1816 except for the continuation of the property tax. On 14 Mar. he suggested the substitution of a tax on absentees from ‘their country’ which he said would raise £700,000 a year; but if ministers could convince him of their case he would support it—otherwise he would abstain. As he later boasted to his constituents, he voted against the tax, 18 Mar. On 13 May he raised a laugh in the debate on the aliens bill when he suggested that absentee compatriots should be recalled on penalty of forfeiting their estates. He was eager to prevent the circulation of forged banknotes, 24 Apr. 1816, and called for the protection of the public by making the Bank liable for them, 7 May. His attempts to pursue the subject were frustrated, but on 1 May 1818 he rejoiced that the House was prepared to deal with the problem and willingly supported Mackintosh’s motion for an inquiry into such forgeries, 14 May. He thought that victory should be celebrated by building new churches rather than by erecting monuments, 25 June 1816. He supported ministers on the composition of the finance committee, 7 Feb. 1817, and paired in favour of the salt duties, 25 Apr., and of the suspension of habeas corpus, 23 June. He was an opponent of the savings bank bill, 23 May 1817. On 10 June he secured the abolition of the punishment of whipping for women, as practised in Inverness. He published his speech of 25 June 1817 in favour of the repeal of the Test Acts: his motion was delayed until 7 May 1818, when it was frustrated. He voted against censure of the Scottish law officers, 10 Feb. 1818, and next day in defence of government employment of agents provocateurs. He supported the Duke of Clarence’s marriage grant, 15 Apr., and the repeal of the usury laws, 21 Apr. He favoured steps to discourage the sale of radical literature, 21 May, and on 3 June 1818 opposed Brougham’s motion for inquiry into popular education.
Thornton was left without a seat in 1818, his patron having died the year before. His farewell address to his constituents, 10 June, referred to his ‘regular attendance ... without the absence of a single day’; to his championship of female offenders in Scotland; and to his hostility to the property tax, based on the maxims of ‘the immortal Burke’.
