Simon - some areas have a local index - these tend not to be complete, but in some cases they include maiden names before the date they were put on the GRO index. UKBMD has listings of these (see the county list on the left of the link) - several use the same software & can be searched together:
http://www.ukbmd.org.uk/Name changing may have been informal, but some were published in the official gazette - these are online & free to search via:
http://www.gazettes-online.co.uk/Those I've found in there have been anglicisations of "foreign" names, but there are others. The National Archives has some information about the various methods & what you might find:
http://www.nationalarchives.gov.uk/records/research-guides/change-of-name.htmCould there have been a divorce that caused talk at the time? The National Archives have some divorce records, searches can be done online, but you need either to visit or to order copies (at a charge):
http://www.nationalarchives.gov.uk/records/looking-for-person/divorce.htmNewspapers may offer clues, either by birth marriage or death announcements or via reports of other matters. Other than some of the nationals there's not much 20th century material online yet. The British Newspaper Archive has some from the early years & is being added to regularly - free to search, but there's a charge to view the images:
http://www1.britishnewspaperarchive.co.uk/