There's no George Gifford listed under that reference - the Gifford family on HO107/1764 folio 435A is:
High St, Hardwick, Cambs
John Gifford head marr 35 farmer & publican 27 acres b Comberton Cambs
Jemima Gifford wife 35 b Swavesey Cambs
Richard John Gifford son 8 b Hardwick
Jane Jemima Gifford dau 4 b Hardwick
Caroline Elizabeth Gifford dau 2 b Hardwick
Ann Moule servant 16 General servant b Hardwick
Whilst Hardwick parish register has been extracted onto the IGI their only child who appears as a baptism is Marianne on 1 Jan 1854. They did however register the births of their children as checking http://www.freebmd.org.uk/cgi/search.pl
I can see the births of Richard in the Sept 1843 quarter in Caxton registration district, which includes Hardwick, then Jane Jemima in Sept 1846, and Caroline in Dec 1848
There's really no time for George to have been born to these parents in 1843 with Richard having been born somewhere between July and September in the same year, and his absence from the census makes me doubt if you have the right family.
FreeBMD shows a George Gifford born in the March quarter 1841 at St Ives and another in 1843, also in the September quarter, in Ely.
The only one I can see in 1851 is George age 7, son of John and Elizabeth living in Littleport Cambs, which is in Ely registration district, so seems to be the 1843 birth.
What evidence do you have that this John and Jemima had a son George in 1843?