Where can I travel with single entry UK visa? I have a Schengen visa as well. If I possess a single entry UK visa, can I travel to Schengen zone from London and return to London? I am an Indian passport holder.
Once you cross the UK borders, your visa is considered "used".
Since yours is only for a single entry, it is no longer valid for entry. You can stay in the UK as long as the provisions of your visa permit, once you exit the UK - you will need a new visa.
As the UK is not party to Schengen, your Schengen visa is not valid for entry into the UK.