When the defendant, at any stage of such action, files a statement in open court consenting to a sum at which the buildings and improvements and the value of the demanded premises may be estimated, if the plaintiff consents thereto, judgment shall be rendered accordingly, as if such sums had been found by verdict; but if the plaintiff does not consent, and the jury does not reduce the value of the buildings and improvements below the sum offered, nor increase the value of the premises above the sum offered, he shall recover no costs after such offer; but the defendant shall recover his costs after such offer and have judgment and execution therefor, subject to section 6965.