Land valuation query

[One More Solo]

Our garden adjoins a patch of woodland that is not part of our title deeds but has been used by previous occupants of the house as an extension of the garden. It's approximately 0.25 acres. We've approached the landowner about buying it and they're open to discussion, but have put it to us to name a price. The land does not have planning permission and it is very unlikely to be granted - it's green belt and is also subject to a tree protection order.

While not giving us a guide price, the landowner has indicated our offer should take into account the fact it would add to the value of our house, which is fair enough. He seemed to think it would add £40-50k which seems bonkers to me but felt like more like an opening gambit than a serious proposal!

My question is, who would be best placed to give us a value for the land? An estate agent?

 

[One More Solo]

Thanks @Martynt74. My thinking was similar that the additional area would probably add negligible value to our house so would be an odd way of valuing it - we already have a large garden and paddock so it doesn't materially increase our outdoor space, and it is very shaded so has limited "amenity" use. We have no interest at all in building on it, but I think the chances of getting planning permission are next to nil so that would massively reduce its value to a third party. I think that is a factor in the owner's willingness to sell.

Acquiring it is more for our own piece of mind than any plans to do anything with it.