Hi Rosie,
Yes, Aldershot registers are at the Surrey FHC. The church in which I want the look-up done is Aldershot Holy Trinity. The Surrey FHC publishes an on-line list of its parish register holdings. Aldershot Holy Trinity registers are on microfilm or microfiche at the Surrey Family History Centre. Aldershot is indeed in Hampshire, but falls within the Farnham (Surrey) Registration District.
How do I know that the marriage sought is at Aldershot Holy Trinity ? I am experienced at "marriage mining" techniques, which take advantage of the fact that Anglican churches are arranged quasi-alphabetically in the marriage registers of the General Register Office. I say "quasi alphabetically" because the ancient parish church often takes preference. Here, the parish church of Aldershot (St Michael) takes preference over Holy Trinity, which is followed by Ash. Aldershot, being a substantial town, would have a large number of marriages, and that is why I am confident that the marriages at Holy Trinity will run from GRO pages 221-229 (page 230 is blank) and thereby include the marriage that I seek at GRO page 227. It probably took place at around 25th December 1906, as it is near to the end of the page range quoted. Check it out and see whether I am right ! I would be very grateful.