When we bought our house the solicitor pointed out that the land behind (advertised as the garden) was actually owned by someone else. The house was built in 1990 and we have lived here 12 years. Can we put up a fence, or claim the land as our own? Could the owners build a house on it?
If the land has been cultivated by you and the previous owners you may be able to claim ownership, although fencing it off is usually regarded as the best means of asserting authority over a piece of land. You should take a photograph of the plot and show it to a solicitor. Is it registered at the Land Registry? That would tell you who owns it. It’s possible you will have taken out indemnity insurance, but the owner could possibly build a house on the plot subject to planning permission.