When you double click the tray icon the default action is to bring up the resident scanner settings. To start the on-demand scanner you need to right click and select “Start avast! antivirus”.
Is there any way to change this default behaviour?
Most users I install avast! for are not comfortable with changing any settings, but they like to be able to run the on-demand scanner easily.
Doesn’t double clicking the desktop icon start the main program?
Don’t use the desktop at all 
It’s disabled. Only the Start-menu.
But the avast! icon is there always visible. And why is the realtime-scanning configuration the default (that’s not what you adjust every day)
Sorry - I don’t know of a way to change the way the system tray icon works, but would a quick start icon do any good?
This was suggested, and suggested, and suggested…
There are pros and cons about this. Anyway, Alwil decision after all…
I’d rather have double clicking the tray icon do NOTHING that it opening the settings. It’s far to easy for the non-techies I install for to mess up something (ok, I can password protect the setting, but but but…)
Ok - if you turn off the tray icon in the avast! settings, make a quick launch icon, and slide quick launch to the right - will this accomplish what you need? The only difference would be single click versus double click.