I've been doing some research in Reading library. On the 1851 census index for Hendred sub-district ref HO107/1689, ref. 501 (East Ginge) I found:

Thomas Champ 27
Caroline Champ 27
Elizabeth Champ 1 month

Also ref. 501 are:

John Champ 58
Harriet Champ 50 (a 2nd wife??)

I also looked in the West Hendred parish register transcript. I found Thomas Champ son of John Ann bapt. 4 Aug 1823 and also James bapt. 3 Aug 1826. However there is a burial for James aged 2 on 29 Sep 1828.

There is a baptism for John Champ son of Richard and Hannah on 14 Oct 1792, date of birth 21 Sep 1792. This ties up with the age of the John living with or near Thomas Caroline on the census (carried out in Mar-Apr 1851). This John also had a brother Thomas bapt. 14 Apr 1791, born 8 Apr 1791.

There are also burials for Hannah (4 Feb 1832 aged 68) and Richard (3 Nov 1832 aged 69), both of East Ginge.

I found the following marriages on the IGI:

John Champ m Ann Bradley
20 Jun 1814 East Hendred, Berkshire

Richard Champ m Hannah Goodanuff
20 Nov 1783 East Lockinge, Berkshire

All of the above villages are within a few miles of each other, and it was (and still is) usual for English weddings to take place in the bride's family's home parish.

Ihaven't yet found any other definite leads or connections to this family, but there were certainly a lot of Champs in the area. As our Martha Champ was married in West Hendred (to Daniel Dawson in 1816), it is possible there could still be a connection between her and your John, maybe cousins or possibly even brother sister (she was born about 1795, supposedly in Didcot, but I haven't found a baptism)?

Also, it's possible that your Sally Allum could be related to our Anne Allum (m. Benjamin Mills 1819 in Sutton Courtenay, again no baptism found).

My e-mail address is kevin.scott@virgin.net. I'll let you know if I find anything else that looks promising, or of course if I do find that missing link that connects our research!

Jenie Scott