Is there any way to display time in UTC on the panel?
The GNOME clock applet, can't display two times on the panel, but it can show two times in the drop down.
Right click on the clock and select "Preferences." Goto the "Locations" tab and press "add."
Then, select "Greenwich Mean Time" from the "Timezone" list.
You can't do it with 2 clocks AFAIK (the clock always shows the time in the local timezone by default), but you can add extra locations in the drop-down menu of the clock applet so that seeing UTC is one click away (this is not yet possible with indicator-datetime though, although I think it's planned).