Right to light is a form of easement in English law that gives a long-standing owner of a building with windows a right to maintain the level of illumination. It is based on the Ancient Lights law. The rights are most usually acquired under the Prescription Act 1832.

In the first instance contact your local District Council.

An earlier suggestion that there may be a clause in the Deeds preventing the parking of motorhomes is, on the face of it, a reasonable suggestion but first you have to contact the landowner who placed the Covenant on the land originally and get them to prosecute. From personal experience I have found this to be virtually impossible as landowners are difficult to trace and even then why would they go to the expense of enforcing the Covenant when there is nothing in it for them?

If it's a local authority property that would be much much easier as they are far more willing to enforce covenants they impose.