Our Secret Garden - Advice Needed Please

I entered into an AST Tenancy agreement with the Letting Agent in 2015. We were shown around the property (A two bed flat) and were pleasantly surprised by the 70-foot garden adjoining the property. During our term we noticed a “Garden” at the back of our property adjoining “Our” Garden and the neighbours garden below us. It was quite overgrown and there was no access to it from our garden. The neighbour below seemed to be quite comfortable popping in and out of it and even propped ladders up against the fence to watch the “Wildlife”. It was also missing fence panels.

Last year the neighbours moved out and a new neighbour moved into the flat below. This is when we learned that the Garden belongs to the property we are renting. However, there is no mention of it in the inventory/description and it was certainly not mentioned by the letting agent.

I contacted the Letting Agent and they were unsure but spoke to the Landlord who confirms “That the land belongs to him and that the previous tenant did not use it”. In the meantime, it has become a dumping ground for building materials from the new neighbour and rubbish from the old neighbour. We have written to the Letting Agent about our concerns, that we will be made responsible for it. As we are due to leave our current property, this has become an issue that we disagree on.

Any advice would be welcome.