My fourth great grandmother letitia smith claimed on census to have been born in stoney Stratford bucks trees on ancestry give dates either 1805 or 1811
What I can’t find is any birth or baptism for letitia.
Stony Stratford, now part of Milton Keynes, lies on the old A5 Watling Street. It had an Eleanor Cross and was an important stop for the coaches that plied Waling Street before the railway and then the M1 changed transport patterns.
The eastern side of the town was originally in the parish of Wolverton and the western side in the parish of Calverton - have you checked Calverton and Wolverton for a baptism for Letitia?
A Romany family the Biddles used to be a familiar sight in Calverton until well into the 20th Century. There are other regular stopping places in the area so look at Beachampton too.
I just looked at the name index in my copy of Richard Edmund's "Early British Gypsy Families" volume 3 which covers SMITH and there's no entry for any Letitia.
There are mentions of Nehemiahs - a possible baptism 1787 Burwell, Cambs, an entry on the 1861 census camped at Grindstone Lane, Edgbaston, Warwicks and in 1841 a Nehemiah Smith and a John Smith imprisoned for lodging under a tent at Long Buckby, Northants.