My neighbour has encroached three hundred square feet land belong to me when he constructed his house. He said that at the time of construction the lekhpal conducted measurements and demarcated my land. I think that he is telling lie. When I made some inquiry from the development authority, the fact revealed that the site plan my neighbour submitted is describing exact land written in the sale deed. In this situation what is the possibility to take back my land.
You have enough evidence to prove that your neighbour had dishonestly encroached your property. He had information about his land, but he deceitfully captured your barren land. In this situation you should lodge an FIR against him for the offence of criminal trespass, which is punishable under section 447 of the Indian Penal Code.
You should also file a complaint before the development authority for the demolition of illegal construction, which is constructed by your neighbour on your property. In the meantime if your neighbour is still planning to build something to avoid your interference then you can get injunction order from the civil court by filing a civil suit under order 39 of the CPC.

