This could be the marriage of George, the witness in 1839
21 February 1842, at St. Pancras, some difficult writing here
George Leach, Bachelor, Harness Maker, father Will Leach, Harness Maker
+
Matilda Collings, Spinster, father J Collings, Builder (I think!)
Both of full age, residence Platt St (?)
Witnessed by Wm (probably!) Leach, Sophia Collings
Birth of a son George in 1849
LEACH, GEORGE
Mother's Maiden Surname: COLLINGS
GRO Reference: 1849 S Quarter in SAINT PANCRAS Volume 01 Page 289
Baptism of George, 14 October 1849, St Pancras
He was born 2 September.
Parents George & Matilda Leach
Abode Judd St
Father a Harness Maker
They are in Judd Street in 1851, over two pages.
George Leach is 34, born Middlesex Bloomsbury. Occupation Army accoutrement maker
For some reason transcribed as Leash in places
https://www.familysearch.org/ark:/61903/1:1:SGTN-QWVGeorge and Matilda are easy to find in the following census years, i.e. 1861 when George is 44, born St. Pancras
https://www.familysearch.org/ark:/61903/1:1:Q2M2-YXYY