Looking at the Beds FHS Surnames interests CD it seems the marriage was in 1793 & by licence. I haven't got sight of the Luton marriage transcripts, however the marriage licence allegations transcripts show the following:-
Marriage on 5 Feb 1793 of Ann Roberts of Luton, age 22, to marry Isaac Ivory of Kimpton, Herts, age 22 - surety given by John Roberts of Luton.
Also Isaac Ivory, gent of Kimpton, Herts gave surety for marriage on 10 Jan 1793 of Isaac Haydon of Luton to Hannah Roberts of Luton, age 25.
There is also marriage on 6 Apr 1793 of Sarah Ivory of Kimpton, Herts age 19 with guardian's consent to George Davison age 19 of Luton - surety given by Abel Ewington, of Kimpton, Herts, guardian of Sarah Ivory.