Thank you - the index has been produced by someone else, now deceased, and is in three separate documents. I've converted these from pdfs to text files, cut and pasted them into one document, then highlighted all the text and clicked the sort button. This puts all the individual letters together correctly but doesn't work within a single letter. I didn't realise the text had to be in a table format for the sort to work. I've just converted it to table and re-run the sort, but it still doesn't perform the sort correctly. Here's a portion of the sorted table:
Ellwood, Mr J.C.P. 14;9
Elm Cottage, Stoke Mandeville BU, fence 21;10
Elphick, S. Harold 12;14
Elshof, De, Malden (NL) 20;8
Elswoud, Overveen (NL), folly group 4;3
Eltham, Orangery LO 61;6
Elvaston Moorish Temple DB 72;20
Endsleigh Cottage orné, Milton Abbot DV 62;15
English Garden, Tsaretsyno, Moscow RUS 70;17
English Heritage (EH)61;3 64;3
English Rococo Garden, The (Michael Symes) 63;18
Engravings, Thomas Smith of Derby 65;5
Enstone Grotto OX 67;11
Enville, Gothic Gateway (Sanderson Miller), ST 64;12
Epsom, Temple Banqueting Hall, Hylands SR 72;4
Essex, Gothic Temple, Hatfield Priory 65;5
Essex, Jumbo, Water Tower, Colchester EX 64;8
Etchells, Frederick 69;19
Evans, Carmen 61;19 63;18
Elton CA, temple 44;5
Elton Hall CA, hermitage 44;15
Elton Hall SH, folly group 40;15
Elvaston Castle DR, folly 46;15