Hi all, many thanks for the info!
I have to get ready for work, but to quickly summarise how I see it, there are 2 Thomas Burrells in question, 1 born in Galway, the other in Armagh: I may be able to get more information about the latter from the same source as I got info about the Galway Thomas. It would also be handy if his discharge record could be found.
The discrepancy in age/birth date in the Thomas living with Elizabeth in 1851 can be accounted for age given in the 1851 census being to the nearest 5 years for adults, lower age.
The army Galway Thomas enlisted in Plymouth, which is where Elizabeth was born. I think I have a possible father who worked in the dockyard.
I got the Galway birthplace from a transcript/image of an 1841 inpatient record for a Thomas Burrell at Greenwich Hospital: incorrectly transcribed as Denmure (no such place), actually Dunmore, Galway, which matches up with the St Nicholas Parish. Gives his occupation as clerk, last ship HMS Beagle, which also matches up: Beagle was originally launched May 1820, but only used once -" July of that year she took part in a fleet review celebrating the coronation of King George IV of the United Kingdom, and for that occasion is said to have been the first ship to sail under the old London Bridge" (Wikipedia) - after that she "lay in ordinary" until being refitted as a barque for expeditions.
All this has made my head spin: I've started putting data into a spreadsheet so info for the 21 or 3 Thomases can be compared!
See you later, Graeme