Stick insulated screwdriver in earth socket, releases pin guards. Then as with all multi-meters, the leads are insulated. The pins are far enough apart not to be a concern of shorting together.
Better still for electric shock, undo face plate from wall, measure behind or take shroud from consumer unit and access terminals there.
If the OP hasnt a meter or a friend with a meter, hasnt/doesnt have the confidence to test the voltages. Call in an electrician. Who will in seconds determine whether its the incoming supply to the home or another issue.