When you tell them they will only get paid when the loan closes, they will disappear.If required, the only money you should ever send to the lender is for a credit check.

The Rockcastle Megasite is an example of a site ready property & is only 20 minutes north of London. https://dataispower.org/rockcastle-mega-site/. 

Not sure what the demand drivers are. 

Another idea would be to ask if they would allow you to visit the place to see what offerings other landlords have in the area.

There are not a ton of comps on Zillow or other websites that I have checked and it was last sold a while ago so even these resources are unable to give me a quote.  

Quote from @Dennis McNeely: In a sandwich lease option, the investor exercises their option with the property owner to purchase the property when the tenant-buyer indicates they're ready to exercise their option and purchases the property.

Plus the hours of material participation. 

Very exciting you are looking to get into the RE investing world.Thanks for the interest in Rent To Retirement.

Send them a written notice of non-renewal, following your local laws about how much notice you need to give.

The following day I got a small counter back and I accepted.