My other car is insured with Admiral for about £500, so I contacted them to ask about adding the Defender on. They quoted me another £500, including mirrored NCB. Lancaster quoted me about £250 with no NCB, so the two car policy didn't work for me in this case.
I suppose my advice would be don't assume that it'll be cheaper to insure both cars on the same policy, especially if one of them is a Land Rover. Talk to the specialists like Lancaster first.