About an hour after posting here I received an email from Google saying they were sorry for the confusion etc and that they had reset my secondary email address to the one I had written to them from. This was in response to a few forms I filled out more than once on their site with as much info as possible that I could inlcude.
So the instructions in the email tell me to go through the lost password steps and click the link to send the password to my secondary email address, then follow the instructions in the email that gets sent.
So it’s been a few hours now, and no email has come to my secondary email address, despite after clicking the link it tells me an email with my password was sent to my secondary email address at blah domain (which is correct).
So back to the drawing board I guess…