Thanks for confirming that I couldn't find a 'default' password :-)
I had another look and discovered that the issue lay with the Password Manager LastPass. As its default it looks at the url and sees a field called password and then puts in a password, not sure which one it took. Deep in LastPass settings is a checkbox 'disable autofill', tick it and then all OK !!
I'll follow up with your other tips, thanks for a good service