Gortonboy and t mo,
Thanks for your help!
All I know is John was born in Ireland sometime around 1798-1801 according to the census records I have for him. He is living in Hampton in Arden, Warwickshire in 1841 with Catherine and son William and then Harborne, Staffs in 1851 with Catherine, William and daughter Mary Ann. In both of these he is recorded as Chelsea Pensioner. The children were both born in England. The earliest record I have is for daughter Elizabeth's Baptism in Coventry in 1838.
He seems to have worked for the railway as I've found from kids' Christening records/censuses doing various jobs such as labourer, railway policeman and timekeeper. Catherine was also born in Ireland but slightly later in around 1806. They disappear completely after the 1851 census.
I'm afraid that's all the information I have. I googled John Armstrong Catherine Costeller marriage and it came up with a couple of unofficial sites listing the two of them separately as being married on Corfu. They both had 1 72 next to their names so I thought this might possibly link them.
Thanks again, Lucy