See RBI guidelines on this matter: (
https://www.rbi.org.in/scripts/FAQView.aspx?Id=33)
"Q.29. Can a person who had bought immovable property, when he was a resident, continue to hold such property even after becoming an NRI/PIO? In which account can the sale proceeds of such immovable property be credited?
Ans. Yes, a person who had bought the residential / commercial property / agricultural land/ plantation property / farm house in India when he was a resident, continue to hold the immovable property without the approval of the Reserve Bank even after becoming an NRI/PIO. The sale proceeds may be credited to NRO account of the NRI /PIO."
Seems to imply you need to be a resident in India to acquire any agricultural land. I am not an expert on this, but since you are a resident in UK now I doubt its legal to buy this proposed land. Also suggest get a legal opinion on this.
Experts please comment.