Thanks everyone. The cottage doesn't have a roof, or even the remnants of a roof, just one gable wall. The other has half fallen down. The space inside the walls has long returned to nature. It is full of rockets in May and there's a beautiful 6ft tall 10 ft wide flowering hebe shrub that grew from a cutting my grandmother literally flung in there, when we had use of the cottage half a century ago. This is now trailing out the 'door' into my garden and I though I know I've no rights to it, I'd be sad to see it go.
My neighbour is currently using the property has a holiday home, so I probably won't see him again until the summer, but he has said he will send a copy of the plans to me. As I'm a carer I doubt if I could afford engineers or consultants fees, but I'll contact the planning department and see what they say.