The site of the former Royston High School is likely to be sold for £7m, the Chronicle has discovered.
The valuation emerged in an email from a planning officer to a senior legal officer at the council which was found among documents in the planning file.
The email, dated January 11, 2013, disclosed the agreed fee for the council-owned land by Kier Property Developments - the firm that submitted plans for 143 houses, a petrol station and supermarket kiosk on the site, off Midland Road, in November.
The planning regulatory board makes a decision next month.
If permission is granted, building work is expected to start in July, according to the email.
It also states the proposed foodstore is 'very likely' to be Morrison's.
Objectors have expressed concerns over access and traffic problems.
One said: "The proposed retail offer is not welcome or required. The community is well served for shopping and fuel.
"Any such development would likely threaten the viability of existing business."
He also said there were issues with how the public consultation process had been handled, claiming the proposal shows no evidence that concerns put forward by residents had been addressed.
A spokesman for Kier Property developments said that as far as he's aware no fee has been agreed.
He said: "An operator has not signed up to the site, but there is significant interest."