As previously mentioned, records pre 2005 are available online and are a more readily available source of information if you don't have an exact date or place.
Dawn -- the
indexes are available on line, but the actual
records are not, is that not it?
And the post-2005 records you refer to are also the indexes, not the records?
If something can't be found in the indexes, GRO staff (or local offices where records are held) will do searches of the records they hold for a fee, but members of the public cannot do that.
That's my understanding, anyhow. Since I'm an ocean away and haven't had to figure it out for my own purposes, somebody will correct me if I'm wrong!
So it depends on whether mavistee was wanting to search generally, using indexes, or actually do hands-on searches of the actual records (which can be done for parish records pre-1837 in the relevant offices, of course, as lizdb says).
There has been much discussion in the family history community about the fact that the GRO provides only certified copies of records, for a hefty fee, and whether it should not make records available in non-certified form / viewable on line, but it seems not likely to happen.