So to sum up the state of play at the moment for anyone else who is following this topic. All the children of John Morton and Sophia were registered with mother's maiden name given as Rolfe. It therefore appears that the marriage certificate naming her as Sophia Holford is wrong. If we assume that then the rest of the certificate falls into place; father Robert a cattle dealer, and witness Thomas, who appears to be Sophia's brother (see post by janfurness above). The family of Robert Rolf (sic) is recorded in the 1841 census with Robert, his wife Ann, and three children, Sophia (21), Thomas (15) and James (six months old). They lived in the hamlet of Dedworth, less than two miles away from Morton's butcher's shop. Robert, Ann and Thomas are on the next census record, by then living in Mount Pleasant which seems to identify with Beaumont Cottages, Clewer Fields, Windsor. That would put them just a couple of hundred yards away from where Sophia lived with John.
Robert Rolfe gives his birthplace as Shalford, Buckinghamshire in 1851, but there does not appear to be any such place. There is, however, a Shalford in Surrey, not far from Guildford. Ann, Robert's wife, gives her birthplace as Uxbridge. Sophia gives her birthplace as Addlestone/Chertsey pretty well consistently apart from the entry in 1911 where it is given as Aylesbury. The hunt is now on for Sophia's birth record.