The local authority certainly won't remove it as it is on private land and not their problem.
If at all possible, surreptitiously get it on to public land then inform the DVLA.
Check on the DVLA web site to see if it is SORN . The site is the same one you use to check if a car is taxed. If it is SORN there is very little you can do apart from trying to find the owner and asking him to remove it.
I would put a large notice on it saying that unless it is removed within 14 days you are going to tow it away and scrap it.