Following Leonard back through the census to 1851, it appears his parents were Job and Thirza LONG.
On the 25 Feb 1873, there is a marriage in Charlton Marshall of Leonard (LAWN) to Elizabeth Ann HALL, their ages fit with your Leonard and Elizabeth, Leonard's father is Job (LAWN). Leonard did not sign, he made his mark, so would not be able to see a mistake in the spelling of his surname.
In 1871 Leonard is boarding in Charlton Marshall a few doors away from Elizabeth HALL. To me, this, and the fact there there appears to be no one by the name of LAWN in the area in the census, all points to the LAWN marriage being the one you are looking for.
Jebber