"Does anyone have any idea as to the extent of coverage of the familysearch records for the UK - would I be correct in saying that if there are no parish records there then they are pretty much lost for ever, or are there still lots of other records to be transcribed and put on line?"
Absolutely not!!! By no means all the parish registers of which the LDS have filmed copies have been indexed, but you can locate the films via the catalogue and hire them at your nearest LDS Centre. For some counties (such as Norfolk), the indexing is limited but the registers themselves are available online for manual searching.
Moreover, the LDS do not have copies of all registers. Local clergy vary in their co-operation with the LDS and for some counties the coverage is very slim. Essex is about 30%, for instance, though the Essex Record Office has been digitising its own films and these will shortly be available on line (at a small cost). Another example is Devon, where the ecclesiastical authorities have denied the LDS access to any original registers. Records for that county found on familysearch have been extracted from transcripts (which only cover about 60% of parishes).
Hope this helps