I've got some info on some London DOWLEYs. Likely to be unconnected if you are tracing your line back to Warwickshire etc.
Sarah Hawes NICHOLSON 1778-1817 married Thomas DOWLEY (by whom 8 children). This Sarah's younger sister (Harriet) married Thomas DOWLEY's brother James:
Harriet NICHOLSON 1785-1867 married James DOWLEY (by whom 9 children) (mostly Deptford and Southwark areas)
I'd love to know about any DOWELEY details you find. At the very least it will help me in eliminating other possible suspects around England.
I also wonder if there is any connection between the 1840 marraige info you are after and this death certificste entry I found in FreeBMD recently:
March quarter of 1892 - death of John DOWLEY aged 89- Pershore district (GRO ref: 6c 292)
This man is probably the one in the 1881 census listed as follows: John DOWLEY Age 80, born c. 1801 Warrington, Worcestershire; Licensed Pedlar; Widowed; Lodging at the Court Coventry Arms Inn, Upton Snodsbury, Worcestershire Census ref: RG112931 / 30