Thank you all for your help and suggestions.
I was having a look today and, working on these assumptions:-
that John being 35 in the 1841 census was born between1800 and 1811
that Charles son of John & Ann who was 26 in the 1851 census was born between 1820 and 1825,
and that Mary Ann who was 17 in the 1851 census was born between 1830 and 1834
and that Ann the wife of John who was 44 in the 1851 census was born between 1805 and 1811
and that the marriage of John to Ann took place between 1820 and 1825, ( he would have been under 20 before 1820, and Charles was born no later than 1825)
I have found the following on findmypast.co .uk
Mary Ann Brown baptised 18 May 1834 dau. of John & Ann in Bristol Gloucestershire, no parish shown.
Then I checked on the 1881 census for Mary Ann Clements, as she became, and there she says she was born in St Michaels Parish, Bristol. I have trawled through several times but cannot find a baptism for Charles.
Does anyone know if the records for St Michaels have been transcribed and added to Ancestry? Or anywhere else on line?
Marriages
John Brown to Ann James 13 December 1824 @ St Nicholas, Bristol
John Brown to Ann Lippiatt 19 October 1823 no Parish Given, just Bristol.
Which somewhat ties in with the no named Parish re the baptism of Mary Ann.
I tried checking the batch number of the 1823 marriage, but it gives no more information.
I am totally at a stand with this line, which is probably why I abandoned it years ago!