Plans

[BARRY]

obtaining next doors neighbours plans to check to see if they have bought land belonging to this house

[woofgang]

in the UK your local district council will have a planning department who can help you identify where your boundaries are. Problem is that land doesn't "belong" to a house, it generally belongs to an owner so if a previous owner of the house sold the land to your neighbour, I don't think you can do anything about it

[New Forester]

In the UK the Land Registry keeps records of all land ownership nationally, if the land changed hands within the last few decades. For a small fee they'll tell you. Go to http://www.landreg.gov.uk/ and click on FAQ. Local Authority planning departments generally don't hold ownership information. They do however have Land Charges departments, who keep records of constraints on the land and provide information for Local Searches when you buy a property.