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.
If you go to the Schengen zone and then try to go back to the UK it will be another entry, and as your visa is single entry, you're not allowed. And there is border control at the UK border for passengers arriving from the Schengen zone.
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Since yours is only for a single entry, it is no longer valid for entry.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.