Land rover Discovery 2004, rear right hand side down 2 inches

If you have the coil spring suspension, then your spring for that corner has really sagged[doubtful] I suspect you actually have the rear air suspension ,and the air spring for the Right/Rear has lost air, allowing the rear end to lower down greatly. Usually, you need a new air spring when one develops a leak. You may or may not be able to see the leak with a spray solution of soapy water after the spring is removed for inspection. Sometimes you have to apply about 20psi of air pressure into the spring to inflate it a bit, then put the spring under water in a big enough tank/tub of water to catch the leak that way.