Not sure anyone else ever has this problem but since I've accidentally found a way around it, I thought I'd post it. Of course, this could well be something that has a much easier solution that I just never knew about and somebody smarter than me will comment to let me know how bad my knowledge of technology has really become.
My problem being that when I created this blog, I was (and still do) mostly using a yahoo email address. At some stage I wanted to create a new email address (I have several, some with my real name, some with usernames from various forums or websites, some just used to sign up for newsletter or something that might potentially lead to increased spam etc.) and I decided to use gmail, which lots of people seemed to have taken to using. I have to admit, I really don' like it but I used that address for a couple of things that have become fairly regular (such as organising book club) so I do need to check it regularly. And if I was already logged into my blog I couldn't log into my gmail account without logging out of blogger first. Which kind of irritated me.
Entirely by accident I recently discovered a workaround though. If I'm logged into blogger and open a new window (or tab), go to youtube and log in there with my gmail account I can then go straight to the gmail site and it will open my email. Without making me log out of blogger first.
So there you have it. I may be the only person that had that problem or found it annoying but that's how to get around it if you need to.