Hi
the banns would give you the date they were called - three successive Sundays before the marriage. As they were both of the parish, at least for the three weeks residency before the marriage (it was expensive to have banns called so often one partner moved to the other's parish for the three weeks to avoid the cost of paying for banns to be called in two churches) and there is no indication either was under age that would be all the information given.
It was traditional that the marriage took place in the bride's parish but in London with lots of newcomers and people working away from home, particularly women as servants, marriage parishes can be pretty transitory.
Witnesses in London marriages are often friends, workmates or parish clerks and not relatives.
Regards
Valds
