Many thanks, everyone, for input. Here is a summary of information on John from second marriage cert and the census (I can't in fact find him in 1851; sorry for error):
2nd marriage:
7th March 1859 at St Martin, Birmingham
John Harris – of full age – Widower – Occupation – Lock Smith – Living at Moor Street – Father – John Harris – Occupation – Soldier
Married
Martha Shaw – of full age – Widow – Living at Moor Street – Father – Thomas Sadler – Occupation – Labourer.
Witnesses are – George Wiseman and Jane Green
http://warwickshireinfo.webspace.virginmedia.com/birmingham_st_martin_marriages_g_to_l.htm1861 RG9/2174, Watery Lane Cottage back of Crown and Anchor, Aston. John, screw bolt turner, b Lye Waste, Worcs, with wife Martha. Also present are Martha's two children, Samuel and Louisa (age 12 and 7). Martha's birthplace is listed as Newport, Salop.
1871 Lodging with Simkin family, "labour [sic] at screw factory", "back of 207 Watery Lane,Bordesley, Aston (back-to-back cottage], married, aged 67, Martha not present. Was Martha helping one of her children? [not found in FindMyPast census search]
1881 RG11/3009 Devonshire St ("16Bk66" - assumed to be back-to-back cottage), Birmingham All Saints. John aged 76 and wife Martha age 69; grand-daughter Eliza E Jones aged 9, born Birmingham (Births Dec 1871 6d 13)
Son William was born c 1829 in Birmingham according to the 1851 census.
1841 census (tentative identification)107/1142/3 Birmingham St Martin's, Bordesley St, William age "15" with Francis Tandy (labourer, "45") and Sarah ("50"); neither Francis nor Sarah b Warwickshire. Marriage (at Handsworth, Staffs) found for this couple (1824); Sarah is nee Harris.
1851 census: lodging with Evans family in Coal Pit Lane, Bedford, Leigh, Lancs, and working as a coal miner.
He died age 35 in a workhouse hospital and seems to have been a "rum 'un" according to the local newspaper (he challenged passers-by to bare-knuckle fights, and was fined for drunkenness and breaching the peace and for drinking after hours). His children, born in Leigh between 1852 and 1863, were Mary, Martha, Jane, John, Elizabeth and two Ellens; John and the first Ellen died in childhood.
Thanks again for your help: much appreciated.