Before I added my "Top Of Page" button, I would compose my posts in "Edit HTML" mode, and at the end of each post, I would add
<a href="#Top">>> Top</a>
That gave me a link to the top of the page, since I included an anchor link "Top" inside an HTML gadget, at the top of the page.
That's simple enough, once you get used to adding the code.
There's a caveat here, though.
Having added the code
<a href="#Top">>> Top</a>I have learned, the hard way that I cannot ever edit the post using Compose mode. Any time that I edit the post using Compose mode,
<a href="#Top">>> Top</a>becomes
<a href="http://www.blogger.com/post-create.g?blogID=24069595#Top">>> Top</a>
The only solution was, that any time I created a post, I would add
<a href="#Top">>> Top</a>last. Then, stay in "Edit HTML" for any more editing.
Blogger Engineering has been shown this problem a few times. It's possible that it is deeply embedded in the Blogger code base, and will require much work to be diagnosed.
In my case, I eliminated the need to add anchor links, by adding my "Top Of Page" button. That eliminates 99% of the anchor links, that I add to my posts.
This may be a problem which we have to know about, and avoid causing. Compose and install anchor links, after you finish using Compose mode.