Simpson

6.6.1788 at T Hollis' / 29.12.1789 Simpson, E.T. at T Hollis' / 18.2.1803 Simpson at Lea's / 9.11.1813 Jas Simpson dines / 2.12.1813 Jas Simpson calls / 4.10.1814 M(ary) J(ane) from Simpson / 5.10.1814 again / 10.4.1829 Simpson at Joshua Robinson's
For the James Simpson of 1813 consider James Simpson DNB 1781-1853 advocate and author, who shared Godwin's interest in education, though he was based mostly in Edinburgh. Otherwise I have very little substance here. Still racking my brains to what ET stood for. Lea was a contact of Godwin's brother Joseph (see Box). Nothing probable in British Book Trades Index. See work notes below

Work notes: 
Holden's 1805: Henry S & co merchants 10 Exchange St / Benjn S & son seedsmen 1 College Green / S, Moore & co woollen drapers 66 Dame St / Alex S glover 94 Grafton St / Janes S bookseller Royal Exchange Edinburgh / Wm S solicitor Broad St, St Giles Norwich. Holdens 1811 about 80 Simpsons in trades and about 50 in court / James S surgeon Earl St Chatham Pl / James S cutler 16 Borough / James S attorney 18 Artillery La Bishopsgate St / James S Esq 60 Chancery La