Hi Tony,
Many thanks for the offer of help, it's very much appreciated, - especially as I have no idea how to navigate the TNA website so have little hope of finding any documents I need, ... and I'm on the opposite side of the rock, and can't see myself getting over there in the foreseeable future!
My fellow is James Dixon, born (according to 1841? census) about 1790 in "St Andrew, London". I haven't been able to find his parents &/or any siblings. I
think he married in 1815, to Hannah Maria Howard (who was under-age), in Marylebone, - but if there is any Army record of his marriage, I'm hoping this could be confirmed. They lost a son, John Edward Dixon, and had a daughter, Mariah Eliza, prior to departure with the 4LDs. Shadowsoftime website shows them aboard the "Dunira" in 1820.
James had been Adjutant to the 21st Dragoons, and transferred to the 4th LD shortly before they left for Kaira/Kirkee in India, in 1820. I have found his various promotions in the "Gazette" (eventually became Quartermaster), plus two births in India - George, who died in infancy, and another daughter, Catherine Amelia, who survived. FIBIS also shows the family returning from India aboard the "Sarah" in 1827, and when they got back, James apparently went on half-pay to the (I think?) 104th Foot, and three more children were born in England; Emma Louisa, Charles Dalbiac Wildey and Emily Jane. He then retired and became Superintendant of Docks Police, and was living in Poplar, London. I believe he died in 1858.
Hope this is enough to be helpful. Again, anything you could find would be hugely appreciated

Cheers
Deb D