Hi - I'm glad you sorted out the "Quayle".
What exactly is the written information you once mentioned you have, which indicates that there is an IOM connection?

Re. your mother not finding out who her birth parents were until she had to produce her birth certificate on enlistment, my point was - how did she find this cert when she believed she had a different surname? It is possible that she was listed in the adoption index at the GRO even though this didn't start until 1927 - but someone must have thought to look at this. If she was in the adoption index she would have been able to apply for her original birth cert.
If she is not in the index, but was formally adopted pre-1927, there would have been some kind of (probably legal) arrangement made. If not formally adopted, or if fostered, there should be records with the Church involved if the new parents were unrelated to her.

Under "Name, surname, and maiden name of mother" does the cert have Dora Darwell Quayle or just Dora Quayle? What is under "Signature description and residence of informant"?
If the cert. has Dora Darwell Quayle presumably you have searched for a marriage for them in the IOM, although this might have been written to hide an illegitimacy.

I doubt you will find what you want wading through web pages - you need the original records. As Stanley Darwell allowed his name to be entered as father on the cert., I still think he could have been supporting his daughter, and a will for him would be your best bet - especially as he was of independent means.
Sorry, I missed out a "w" on the URL I posted last message. It should be www.genuki.org.uk/big/eng/Probate.html

Sue