Just noticed nannynick posted a screenshot, and I noticed it was different to what I had seen when using Advanced Search.
I see that if using the new layout, compared with "Classic" then the list is alphabetic if looks under "By Time" and then choose "by topic" then an alphabetic list is displayed.
Previously I had been using Classic mode (which I will probably return to) and the layout is quite different. Low on the page are two lists, the left being the full complement of topics, the right list empty initially, but is the 'Selected topics'.
Now, my query relates to the left hand list. If it is easy to produce the list alphabetically (as is shown when not using "Classic") then it should equally be possible in Classic mode.
Hope this is clearer, if there had been any confusion before.