We rent a piece of land at the bottom of our garden from the owner of the land.The land is about 40feet by 30feet and we have our garage and shed on this land.The owner of this land is giving us the option to buy the freehold.How much is this land worth.There are about 20 other houseolds in the same situation.
As much (or little) as you are willing to pay. There is no formula for working such a thing out.
You could ask the opinion of a professional valuer for the open market value of your house with and without the piece of extra land, but it would be overkill.
Ask them how much they want you maybe surprised don't forget it's garden not a housebuilding plot a rough guide would be to multiply what you pay per year by 15,but ask first then dicker about it