MAINWARING, William (1735-1821), of Hanover Square, Mdx.

Published in The History of Parliament: the House of Commons 1790-1820, ed. R. Thorne, 1986
Available from Boydell and Brewer



1784 - 1802

Family and Education

b. 6 Oct. 1735, o.s. of Boulton Mainwaring, architect, of Isleworth, educ. Merchant Taylors’ 1744-52; L. Inn 1754, called 1759. m. 1s. 1da.1 suc. fa. 1778.

Offices Held

First prothonotary of ct. of c. p. 1768-94; chairman, Mdx. and Westminster qtr. sessions 1781-1816; bencher, L. Inn 1795, treasurer 1804.

Dir. Equitable Assurance Co., Hudson’s Bay Co.

Capt. Loyal Mdx. light horse vols. 1798.


Mainwaring, the adept manipulator of the Middlesex bench, retained his county seat without opposition in 1790 and 1796. He continued to give general support to Pitt, but his standpoint was essentially independent and his vote could not always be relied on. His attitude resembled that of William Wilberforce and the evangelical Pittite backbenchers. Although he was not a member of the Clapham Sect, was opposed to the repeal of the Test Act in Scotland in 1791 and voted against the abolition of the slave trade, 15 Mar. 1796, he belonged to the Proclamation Society, and in the City, where he and his son became partners in the Cornhill banking house of Mainwaring, Son, Chatteris & Co. in 1799, he moved in the same circle as Wilberforce’s associate, Henry Thornton. An additional, though intermittent, influence on his political conduct was the pressure of public opinion in his constituency.

Selected to move the address, 30 Nov. 1790, he praised ministers’ conduct in the Nootka Sound crisis and added that he would not have undertaken the task ‘if he had not been convinced that the convention was fraught with many of the most happy consequences to Great Britain’. He voted for Harrison’s motion of 8 Apr. 1794 to tax placemen and pensioners. He seems initially to have supported the French war, but voted for Wilberforce’s calls for peace negotiations, 30 Dec. 1794 and 27 May 1795, though he sided with government against Grey’s peace motion of 26 Jan. 1795. He is not known to have cast any further votes against the war and indeed was severely criticized for his support of it at a county meeting in October 1800.2 On 14 May 1795 he claimed not yet to have made up his mind on the question of provision for the Prince of Wales, but he voted for Sumner’s amendment, 1 June, and was the only supporter of the proposal of Thomas Stanley, 15 June, to give the Princess a separate establishment of £5,000 p.a. Although he ‘felt the necessity of speedily adopting some strong and effectual measure for stemming the torrent of sedition’ and therefore voted for the second reading of the seditious meetings bill, 17 Nov. 1795, he expressed strong reservations about certain features of it, particularly its investment of a discretionary power in magistrates and its prohibition of ‘all public lecturing on whatsoever subject, without a licence, whereby the diffusion of useful knowledge would be checked’: accordingly he opposed details of the bill at subsequent stages. In the ministerial survey drawn up for the 1796 general election he was marked ‘doubtful’.

Mainwaring subscribed £3,000 to the 1797 loyalty loan, but was a steady opponent of the assessed taxes augmentation bill, largely in response to constituency pressure, as he admitted in the House, 14 Dec. 1797. He presented petitions for the repeal of the clock and watch tax on 18 Dec. and 11 Jan. 1798 and secured their investigation by select committee, 9 Feb., with the intention of founding a repeal bill on its report. When Pitt agreed to abandon the tax, 12 Mar., he was duly grateful, and exonerated the government from charges of procrastination. His allowance from the secret service fund as chairman of the bench was raised by £400 to £750 in 1799, but the increase reflected only a desire to create ‘a salary proportioned to the trust and labour of the situation’ and definitely not a wish to reward Mainwaring personally, as the secretary to the Treasury explained to Lord Kenyon: ‘with Mr Mainwaring I have no private friendship, and his political conduct on very many occasions (generally the most important) has not recommended him much to favour’.3

In 1795 George Chalmers ranked Mainwaring high among ‘the more useful and respectable members’ of the Commons and the following year a newspaper wrote of his ‘unwearied diligence’ on committees.4 Certainly he was active and assiduous as a private Member. On 6 Mar. 1794 he obtained leave to introduce a bill, backed by Wilberforce and the Proclamation Society, to promote better observance of the Sabbath by empowering magistrates to pay informers’ expenses and to restrict the Sunday working hours of journeymen bakers. Strenuous opposition forced the abandonment of the former provisions, but the amended measure became law on 23 May 1794. He was less successful with his proposed measure of 1797 to prevent the forestalling of live cattle, which was lost by 32 votes to 7, 29 June, when the government came out emphatically against it and Mainwaring sourly remarked that the House ‘was today so much enlightened as to determine on a general principle, against the opinion of the kingdom’. On 27 June 1800 he drew attention to the inability of certain metropolitan parishes to sustain the mounting burden of the poor rates and proposed to remedy the problem by making temporary provision for the richer parishes to supply the deficiency. He was given leave to bring in a bill to levy an additional rate in Marylebone and St. Pancras, 1 July, but even Pitt’s warm support was of no avail against vigorous opposition both inside and outside the House, and the measure was abandoned two weeks later. A frequent speaker on local matters and issues which reflected the problems he encountered as a metropolitan magistrate, he successfully moved amendments to the Westminster police bill of 1792, whereby magistrates were empowered to appoint constables with powers of arrest on suspicion of criminal intent.

Mainwaring transferred his independent support to Addington’s administration. On 23 Mar. 1801 he severely criticized the proposed measure for the improved collection of poor rates. Although he moved the second reading of the coroners fees bill, 23 Mar. 1802, and argued its merits, he felt the need to explain

the part he took in bringing it forward. He knew no reason why he was the person chosen to present it ... but the application was made to him and he had always thought it his duty to bring forward every measure he was desired to do, provided such a measure was not in itself an improper one.

By 7 Apr. he had conceived objections to certain features of the measure and declared his intention of opposing them in committee, ‘notwithstanding he was himself the bringer in of the bill’. It was thrown out on 10 June. Speaking on the budget, 5 Apr. 1802, he welcomed the proposal to drop the income tax but apprehended that ‘this odious tax was to be held as a rod of iron, in petto, over the heads of the people at any future time when the country may have the misfortune to be again involved in war’. For all this, he did not vote against the government in any of the divisions of 1801 and 1802 for which minority lists survive; and on 7 June 1803, when out of the House (but with apparently excellent prospects of a swift return on petition) he wrote to Addington congratulating him on the defeat of Patten’s motion of censure and praising his conduct of affairs, though he repeated his wish for complete abandonment of the income tax.5

When Sir Francis Burdett brought to the notice of the House the treatment of political prisoners in Coldbath Fields prison and charged the governor, Aris, with inhumane conduct and the Middlesex bench with negligent supervision, Mainwaring asserted, 21 Dec. 1798, that

there were none of the abuses stated. The keeper ... was a person of great humanity and attention to his duty, and every care was exerted for preserving the health and comfort of the persons confined. He was sure that there was not a more comfortable place of the kind in the whole country.

As well as instigating the magistrates’ inquiry which reported favourably on the institution early in 1799, Mainwaring consistently defended Aris in the House; even when, in July 1800, Burdett secured a fresh investigation, which substantially vindicated his case, he refused to concede any ground. At the general election of 1802 he was challenged and defeated by Burdett, whose campaign turned almost exclusively on the Coldbath Fields ‘bastille’ and Mainwaring’s association with and defence of Aris and the abuses perpetrated in the prison. He petitioned, but although Burdett was found to have been unduly elected, he himself was deemed to have been guilty of bribery and the election was declared void in 1804. He did not seek re-election to the House.6

Mainwaring’s period as chairman of the Middlesex bench saw the introduction of extensive corruption into the administration of county affairs. The appointment of his son to the treasurership in 1804 gave the family bank access to and custody of substantial public sums. He exploited his position as commissioner of sewers to have certain current accounts transferred to his own bank and in June 1813 moneys from the Haymarket tolls and other sources followed them. Nevertheless, his financial position became increasingly precarious and in January 1814 he applied unsuccessfully to Lord Liverpool for an increase in his allowance, pleading the ‘diligence, integrity and honour’ with which he had executed his duties. On the collapse of the family bank in November 1814, it was discovered that his son owed the county almost £10,000, but Mainwaring survived the scandal and retained his position. So powerful was his control of the bench that when ‘the state of my health, my misfortunes and the inevitable infirmities of old age’ forced him to retire in April 1816, the court officially memorialized the government to grant him a pension from public funds.7 He died 28 Feb. 1821.

Ref Volumes: 1790-1820

Authors: Richard Brown / David R. Fisher


  • 1. Gent. Mag. (1810), i. 179.
  • 2. Courier, 3, 29 Jan. 1795; The Times, 30 Oct. 1800.
  • 3. G. T. Kenyon, Life of Lord Kenyon, 334-5.
  • 4. Parl. Portraits (1795), ii. 100-2; True Briton, 21 Apr. 1796.
  • 5. Sidmouth mss.
  • 6. See MIDDLESEX.
  • 7. Greater London RO, Mdx. Sessions recs. MJ/OC, orders of ct. bks. 3 June 1813, 1 Dec. 1814, 4 Apr. 1816; Add. 38256, f. 27; 38264, f. 7; S. and B. Webb, English Local Govt. i. 562-5.