5.3.1791 at Timothy Hollis /  18.9.1796 at Horne Tooke's
Isaac Preston admitted Lincolns inn 1769, eldest son by 2nd wife of Isaac Preston deceased (will PCC 1768) of Beeston St Laurence Norfolk; subscr to Jebb's Works 1787, Law List 1793 counsel Norfolk circuit, recorder of Lynn, died 6.5.1796, will PCC 1796. Likely the Hollis entry in 1791 but cannot be the Tooke's entry as he was dead.
Just possibles are William Preston DNB 1750-1807 dramatist lived Dublin, Thomas Preston DNB 1774-1850 for the Tooke's entry & William Preston DNB 1742-1818 freemason
19.3.1807 call on Nicholson, for M(ary) J(ane); adv. Preston / 20.4.1819 Ogilvie & Preston call (not seen)
Both these could have been Thomas Preston (DNB 1774-1850) though not especially likely.. A Thomas Preston of Higher Ardwick, Lancashire sent Godwin a long letter re: Malthus dated 4.4.1821 (Bodleian Abinger MS b.1.f.7-8). He appeared in Pigot's 1821 directory as gent of Higher Ardwick and in Baines's 1824 as gent of 5 Leigh-place, Ardwick, but I could find no more about him. Probably not any of the diary Prestons and clearly not Thomas Preston (1774-1850) about whom I have found some information not in DNB. He was bapt at St Sepulchre 20.3.1774 son of Thomas & Ann Preston and the baptism record gave his birth date as 22.2.1774 exactly as stated in Preston's own autobiography (1817). His older siblings were Benjamin born 14.7.1766 bapt 7.8.1766,/ Thomas born 11.6.1768 bapt 3.7.1768 buried 1.4.1771 from Old Baily / Joseph born 23.11.1769 bapt 4.12.1770 all at St Sepulchre. His father's death I couldn't find but it must have happened soon after (or even before) his birth. His mother remarried at St Luke Old St 23.1.1775 as otp wid X her mark to John Osborne otp bach. This is confirmed by the apprenticeship of Benjamin son of Thomas Preston late of Huggin Lane watchmaker deceased to John Osborne of Wood-st London silversmith of Goldsmiths co. on 2.8.1780.  John Osborne appeared in Land tax books at Wood-st till 1790 and then at Staining-lane till 1798. I couldn't find his death or that of Preston's mother, but Geo Solloway of Wilsted-pl St Pancras cordwainer took appr Thomas Preston on 15.9.1788 for 7 yrs premium 5 gns. Benjamin Preston seems to have become an assayer or "weigher-in" at Goldsmiths Hall (Old Bailey 1813) and was living at Park-pl Peckham in the 1841 census age 70, Independent means. Thomas Preston's marriage to a widow was possibly at Islington on 1.12.1801 as bach otp to Mary Best X her mark otp wid. Four children were baptised as theirs; Sophia (said tto be born 1799) and Ann on 2.8.1802 at Holborn from Field-lane / Susannah born 2.9.1803 bapt 27.9.1803 at St Jas Clerkenwell / Thomas born 26.2.1805 bapt 26.3.1805 at St Jas Clerkenwell and buried there 5.11.1805 age 8 mos from Mutton Hill. The four daughters Preston was left with when his wife ran away to America in 1807 may have included one by her former husband (and maybe Sophia was too). But I found no record of their subsequent lives, nor could I find any trace in ratebooks, Land tax or directories of the shops Preston claimed to have run in Swallow-st and High Holborn. Preston was perhaps the Thomas Preston shoemaker age 70 living at Little Whites Alley, Liberty of the Rolls in the 1841 census with William Islington tailor age 45 Susan Preston age 50 James Forrester shoemaker age 20 and William Forrester porter age 20. Susan Preston was at 27 Ship-yard in 1851 census as widow age 63 born Bungay Suffolk with James Forrester unmarried age 30, her son in law (must mean stepson) born Battle Bridge Pentonville. Preston was buried 9.6.1850 at Bunhill Fields from 18 Benjamin-st Clerkenwell age 82 (in fact he was only 76)